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layout: blog_detail
title: "Understanding LazyTensor System Performance with PyTorch/XLA on Cloud TPU"
author: Vaibhav Singh
featured-img: ""
Introduction
Ease of use, expressivity, and debuggability are among the core principles of PyTorch. One of the key drivers for the ease of use is that PyTorch execution is by default “eager, i.e. op by op execution preserves the imperative nature of the program. However, eager execution does not offer the compiler based optimization, for example, the optimizations when the computation can be expressed as a graph.
LazyTensor [[1]], first introduced with PyTorch/XLA, helps combine these seemingly disparate approaches. While PyTorch eager execution is widely used, intuitive, and well understood, lazy execution is not as prevalent yet. | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
In this post we will explore some of the basic concepts of the LazyTensor System with the goal of applying these concepts to understand and debug performance of LazyTensor based implementations in PyTorch. Although we will use PyTorch/XLA on Cloud TPU as the vehicle for exploring these concepts, we hope that these ideas will be useful to understand other system(s) built on LazyTensors.
LazyTensor
Any operation performed on a PyTorch tensor is by default dispatched as a kernel or a composition of kernels to the underlying hardware. These kernels are executed asynchronously on the underlying hardware. The program execution is not blocked until the value of a tensor is fetched. This approach scales extremely well with massively parallel programmed hardware such as GPUs. | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
The starting point of a LazyTensor system is a custom tensor type. In PyTorch/XLA, this type is called XLA tensor. In contrast to PyTorch’s native tensor type, operations performed on XLA tensors are recorded into an IR graph. Let’s examine an example that sums the product of two tensors:
import torch
import torch_xla
import torch_xla.core.xla_model as xm
dev = xm.xla_device()
x1 = torch.rand((3, 3)).to(dev)
x2 = torch.rand((3, 8)).to(dev)
y1 = torch.einsum('bs,st->bt', x1, x2)
print(torch_xla._XLAC._get_xla_tensors_text([y1]))
You can execute this colab notebook to examine the resulting graph for y1. Notice that no computation has been performed yet.
y1 = y1 + x2
print(torch_xla._XLAC._get_xla_tensors_text([y1]))
| https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
The operations will continue until PyTorch/XLA encounters a barrier. This barrier can either be a [mark step()](https://github.com/pytorch/xla/blob/ff079bb48744e5aa6696201ccf34057f15fc7cac/torch_xla/core/xla_model.py#L751) api call or any other event which forces the execution of the graph recorded so far.
```python
xm.mark_step()
print(torch_xla._XLAC._get_xla_tensors_text([y1]))
Once the mark_step() is called, the graph is compiled and then executed on TPU, i.e. the tensors have been materialized. Therefore, the graph is now reduced to a single line y1 tensor which holds the result of the computation.
Compile Once, Execute Often | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
Compile Once, Execute Often
XLA compilation passes offer optimizations (e.g. op-fusion, which reduces HBM pressure by using scratch-pad memory for multiple ops, ref ) and leverages lower level XLA infrastructure to optimally use the underlying hardware. However, there is one caveat, compilation passes are expensive, i.e. can add to the training step time. Therefore, this approach scales well if and only if we can compile once and execute often (compilation cache helps, such that the same graph is not compiled more than once).
In the following example, we create a small computation graph and time the execution:
y1 = torch.rand((3, 8)).to(dev)
def dummy_step() :
y1 = torch.einsum('bs,st->bt', y1, x)
xm.mark_step()
return y1
%timeit dummy_step
The slowest run took 29.74 times longer than the fastest. This could mean that an intermediate result is being cached.
10000000 loops, best of 5: 34.2 ns per loop
| https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
10000000 loops, best of 5: 34.2 ns per loop
```
You notice that the slowest step is quite longer than the fastest. This is because of the graph compilation overhead which is incurred only once for a given shape of graph, input shape, and output shape. Subsequent steps are faster because no graph compilation is necessary.
This also implies that we expect to see performance cliffs when the “compile once and execute often” assumption breaks. Understanding when this assumption breaks is the key to understanding and optimizing the performance of a LazyTensor system. Let’s examine what triggers the compilation.
Graph Compilation and Execution and LazyTensor Barrier | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
We saw that the computation graph is compiled and executed when a LazyTensor barrier is encountered. There are three scenarios when the LazyTensor barrier is automatically or manually introduced. The first is the explicit call of mark_step() api as shown in the preceding example. mark_step() is also called implicitly at every step when you wrap your dataloader with MpDeviceLoader (highly recommended to overlap compute and data upload to TPU device). The Optimizer step method of xla_model also allows to implicitly call mark_step (when you set barrier=True). | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
The second scenario where a barrier is introduced is when PyTorch/XLA finds an op with no mapping (lowering) to equivalent XLA HLO ops. PyTorch has 2000+ operations. Although most of these operations are composite (i.e. can be expressed in terms of other fundamental operations), some of these operations do not have corresponding lowering in XLA.
What happens when an op with no XLA lowering is used? PyTorch XLA stops the operation recording and cuts the graph(s) leading to the input(s) of the unlowered op. This cut graph is then compiled and dispatched for execution. The results (materialized tensor) of execution are sent back from device to host, the unlowered op is then executed on the host (cpu), and then downstream LazyTensor operations creating a new graph(s) until a barrier is encountered again. | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
The third and final scenario which results in a LazyTensor barrier is when there is a control structure/statement or another method which requires the value of a tensor. This statement would at the minimum cause the execution of the computation graph leading to the tensor (if the graph has already been seen) or cause compilation and execution of both.
Other examples of such methods include .item(), isEqual(). In general, any operation that maps Tensor -> Scalar will cause this behavior.
Dynamic Graph
As illustrated in the preceding section, graph compilation cost is amortized if the same shape of the graph is executed many times. It’s because the compiled graph is cached with a hash derived from the graph shape, input shape, and the output shape. If these shapes change it will trigger compilation, and too frequent compilation will result in training time degradation.
Let’s consider the following example:
```python
def dummy_step(x, y, loss, acc=False):
z = torch.einsum('bs,st->bt', y, x) | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
z = torch.einsum('bs,st->bt', y, x)
step_loss = z.sum().view(1,)
if acc:
loss = torch.cat((loss, step_loss))
else:
loss = step_loss
xm.mark_step()
return loss
import time
def measure_time(acc=False):
exec_times = []
iter_count = 100
x = torch.rand((512, 8)).to(dev)
y = torch.rand((512, 512)).to(dev)
loss = torch.zeros(1).to(dev)
for i in range(iter_count):
tic = time.time()
loss = dummy_step(x, y, loss, acc=acc)
toc = time.time()
exec_times.append(toc - tic)
return exec_times
dyn = measure_time(acc=True) # acc= True Results in dynamic graph
st = measure_time(acc=False) # Static graph, computation shape, inputs and output shapes don't change
import matplotlib.pyplot as plt
plt.plot(st, label = 'static graph')
plt.plot(dyn, label = 'dynamic graph')
plt.legend()
plt.title('Execution time in seconds')
```
| https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
Note that static and dynamic cases have the same computation but dynamic graph compiles every time, leading to the higher overall run-time. In practice, the training step with recompilation can sometimes be an order of magnitude or slower. In the next section we discuss some of the PyTorch/XLA tools to debug training degradation.
Profiling Training Performance with PyTorch/XLA
PyTorch/XLA profiling consists of two major components. First is the client side profiling. This feature is turned on by simply setting the environment variable PT_XLA_DEBUG to 1. Client side profiling points to unlowered ops or device-to-host transfer in your source code. Client side profiling also reports if there are too frequent compilations happening during the training. You can explore some metrics and counters provided by PyTorch/XLA in conjunction with the profiler in this notebook. | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
The second component offered by PyTorch/XLA profiler is the inline trace annotation. For example:
import torch_xla.debug.profiler as xp
def train_imagenet():
print('==> Preparing data..')
img_dim = get_model_property('img_dim')
....
server = xp.start_server(3294)
def train_loop_fn(loader, epoch):
....
model.train()
for step, (data, target) in enumerate(loader):
with xp.StepTrace('Train_Step', step_num=step):
....
if FLAGS.amp:
....
else:
with xp.Trace('build_graph'):
output = model(data)
loss = loss_fn(output, target)
loss.backward()
xm.optimizer_step(optimizer)
Notice the start_server api call. The port number that you have used here is the same port number you will use with the tensorboard profiler in order to view the op trace similar to:
| https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
Op trace along with the client-side debugging function is a powerful set of tools to debug and optimize your training performance with PyTorch/XLA. For more detailed instructions on the profiler usage, the reader is encouraged to explore blogs part-1, part-2, and part-3 of the blog series on PyTorch/XLA performance debugging.
Summary | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
Summary
In this article we have reviewed the fundamentals of the LazyTensor system. We built on those fundamentals with PyTorch/XLA to understand the potential causes of training performance degradation. We discussed why “compile once and execute often” helps to get the best performance on LazyTensor systems, and why training slows down when this assumption breaks.
We hope that PyTorch users will find these insights helpful for their novel works with LazyTensor systems.
Acknowledgements
A big thank you to my outstanding colleagues Jack Cao, Milad Mohammedi, Karl Weinmeister, Rajesh Thallam, Jordan Tottan (Google) and Geeta Chauhan (Meta) for their meticulous reviews and feedback. And thanks to the extended PyTorch/XLA development team from Google, Meta, and the open source community to make PyTorch possible on TPUs. And finally, thanks to the authors of the LazyTensor paper not only for developing LazyTensor but also for writing such an accessible paper. | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
Refrences
[[1]] LazyTensor: combining eager execution with domain-specific compilers | https://pytorch.org/blog/understanding-lazytensor-system-performance-with-pytorch-xla-on-cloud-tpu/ | pytorch blogs |
layout: blog_detail
title: "PyTorch Conference 2023: Join us in San Francisco October 16-17"
We’re thrilled to announce the upcoming PyTorch Conference 2023! On October 16-17, the conference will showcase PyTorch 2.0, the next-generation release of the popular machine learning framework. As part of the Linux Foundation, the PyTorch Foundation Conference continues the tradition of bringing together leading researchers, developers, and academic communities to advance the education and development of end-to-end machine learning. | https://pytorch.org/blog/pytorch-conference-2023/ | pytorch blogs |
The conference agenda features an engaging lineup of events, including an opening reception, engaging community and partner discussions, informative panels, poster sessions, enlightening use cases and community stories, as well as discussions on the latest trends in machine learning and deep learning development and deployment.
Call for Proposals
We are now accepting speaker proposals for the conference until July 21. The program committee will carefully review all submissions, and selected speakers will be notified by August 8. We strongly encourage both experienced and first-time speakers to submit their proposals. This conference provides an excellent opportunity to connect with the PyTorch community, share your ideas, and showcase your work.
When preparing your proposal, please consider the following guidelines:
* What are you hoping to get from your presentation?
* What do you expect the audience to gain from your presentation? | https://pytorch.org/blog/pytorch-conference-2023/ | pytorch blogs |
How will your presentation help better the open source ecosystem?
To help you shape your proposal, here are some suggested topics for the conference:
Deployments on AWS, Azure
Use cases and real-world applications
Foundational models
AI practices
Production considerations
PyTorch 2.X features and updates
Training techniques and best practices
Inference methodologies
Hardware advancements and optimizations
Edge computing applications
Scalability solutions
Latest research breakthroughs
Optimization strategies
Extending PyTorch through customizations and plugins
We kindly request that you refrain from submitting sales or marketing pitches and avoid discussing unlicensed or closed-source technologies. Such talks tend to detract from the integrity of our events and are not well-received by conference attendees.
Register Today | https://pytorch.org/blog/pytorch-conference-2023/ | pytorch blogs |
Register Today
Registration is now open! Get your ticket today and secure your spot: https://events.linuxfoundation.org/pytorch-conference/register/
Thank you for your interest, and we look forward to a successful PyTorch Conference 2023! | https://pytorch.org/blog/pytorch-conference-2023/ | pytorch blogs |
layout: blog_detail
title: "Accelerating Large Language Models with Accelerated Transformers"
author: Lucas Pasqualin, Driss Guessous, Christian Puhrsch, Bertrand Maher, Michael Gschwind
| https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
TL;DR. We show how to use Accelerated PyTorch 2.0 Transformers and the newly introduced torch.compile() method to accelerate Large Language Models on the example of nanoGPT, a compact open-source implementation of the GPT model from Andrej Karpathy. Using the new scaled dot product attention operator introduced with Accelerated PT2 Transformers, we select the flash_attention custom kernel and achieve faster training time per batch (measured with Nvidia A100 GPUs), going from a ~143ms/batch baseline to ~113 ms/batch. In addition, the enhanced implementation using the SDPA operator offers better numerical stability. Finally, further optimizations are achieved using padded inputs, which when combined with flash attention lead to ~87ms/batch. | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
Recent times have seen exponential adoption of large language models (LLMs) and Generative AI in everyday life. Tightly coupled with these ever-growing models is the ever-growing training cost - in terms of both time and hardware utilization. The PyTorch team has tackled these challenges head on with Accelerated PyTorch 2 Transformers (previously known as “Better Transformer”) and JIT Compilation in PyTorch 2.0. | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
In this blog post, we explore training optimizations gained by utilizing custom kernel implementations of SDPA - also known as scaled dot product attention - a critical layer in transformer models. The custom kernel for SDPA replaces several discrete sequential operations with one globally optimized kernel which avoids allocating a large amount of intermediate CUDA memory. This approach offers a number of advantages, including but not limited to: higher performance computation of SDPA by reducing memory bandwidth bottleneck, reduced memory footprint to support larger batch sizes, and finally added numerical stability by prescaling input tensors. These optimizations are demonstrated on nanoGPT, an open-source implementation of GPT from Andrej Karpathy.
Background
Scaled dot product attention is the fundamental building block of multihead attention, as introduced in “Attention is All You Need”, and has a wide range of applications in LLM and Generative AI models. | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
Figure 1: The Transformer model architecture based on “Attention is All You Need”. With the new PyTorch SDPA operator, Multi-Head Attention is efficiently implemented by a linear layer for the in-projection, the SDPA operator, and a linear layer for the out-projection.
With the new scaled_dot_product_attention operator, multihead attention can be implemented in just 3 steps: in projection with a linear layer, SDPA, and out projection with a linear layer.
```
In Projection
variable descriptions:
q,k,v = Query, Key, Value tensors
bsz = batch size
num_heads = Numner of heads for Multihead Attention
tgt_len = Target length
src_len = Source Length
head_dim: Head Dimension | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
head_dim: Head Dimension
q, k, v = _in_projection(query, key, value, q_proj_weight, k_proj_weight, v_proj_weight, b_q, b_k, b_v)
q = q.view(bsz, num_heads, tgt_len, head_dim)
k = k.view(bsz, num_heads, src_len, head_dim)
v = v.view(bsz, num_heads, src_len, head_dim)
# Scaled Dot Product Attention
attn_output = scaled_dot_product_attention(q, k, v, attn_mask, dropout_p, is_causal)
# Out Projection
attn_output = attn_output.permute(2, 0, 1, 3).contiguous().view(bsz * tgt_len, embed_dim)
attn_output = linear(attn_output, out_proj_weight, out_proj_bias)
attn_output = attn_output.view(tgt_len, bsz, attn_output.size(1))
``` | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
``
PyTorch 2. supports multiple different kernels optimized for specific use cases, with specific requirements. A kernel picker picks the best kernel for a particular combination of input parameters. If no optimized "custom kernel" for a particular combination of input parameters can be identified, the kernel picker selects a general kernel that can handle all input combinations.
While future releases may extend this set of operators, PyTorch 2.0 launches with 3 implementations for the SDPA operator:
1. A generic kernel which implements the mathematical equation of SDPA in the functionsdpa_math()`
2. An optimized kernel based on the paper “Flash Attention”, which supports evaluation of SDPA with 16 bit floating point data types on compute architecture SM80 (A100). | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
An optimized kernel based on the paper “Self-Attention Does Not Need O(n^2) Memory" and implemented in xFormer, which supports both 32 and 16 bit floating data types on a wider range of architectures (SM40 and later). This blog post refers to this kernel as the mem_efficient kernel.
Note that both optimized kernels (two and three listed above), support a key padding mask and limit the supported attention mask to causal attention. Accelerated PyTorch 2.0 Transformers today only support the causal mask when it is specified using the is_causal boolean. When a mask is specified, the general-purpose kernel will be selected because it is too expensive to analyze the contents of a provided mask to determine if it is the causal mask. Additional explanations on the constraints for each kernel can be found in the Accelerated PT2 Transformer blog.
| https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
Enabling Accelerated Transformers with nanoGPT
The SDPA operator being a critical component of the GPT model, we identified the open source nanoGPT model as an excellent candidate for both demonstrating the ease of implementation and benefits of PyTorch 2.0’s Accelerated Transformers. The following demonstrates the exact process by which Accelerated Transformers was enabled on nanoGPT.
This process largely revolves around replacing the existing SDPA implementation with the newly added F.scaled_dot_product_attention operator from functional.py. This process can be easily adapted to enable the operator in many other LLMs. Alternatively, users can instead choose to call F.multi_head_attention_forward() or utilize the nn.MultiHeadAttention module directly where applicable. The following code snippets are adapted from Karpathy’s nanoGPT repository. | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
Step 1: Identify the existing SDPA implementation
In the case of nanoGPT, SDPA is implemented in the model’s CausalSelfAttention class. The original implementation at time of writing is adapted below for this post.
Step 2: Replace with Torch’s scaled_dot_product_attention
At this point we can note the following:
* Lines 36 - 42 define the mathematical implementation of SDPA which we are replacing
* The mask applied on line 39 is no longer relevant since we are using scaled_dot_product_attention’s is_causal flag.
* The dropout layer used in line 41 is also now unnecessary.
Swapping out the SDPA implementation for torch’s scaled_dot_product_attention and removing the now redundant code yields the following implementation. | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
Alternatively, the original mask can be passed into the attn_mask field however due to the mentioned kernel constraints that would limit the implementation to only support the generic sdpa_math kernel.
Step 3 (Bonus): Faster matmuls with padding
On top of the performance improvements from SDPA, our analysis yielded a nice ancillary win. In Andrej's words "The most dramatic optimization to nanoGPT so far (~25% speedup) is to simply increase the vocab size from 50257 to 50304 (nearest multiple of 64)."
| https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
The vocab size determines the dimensions of matmuls in the output layer of GPT, and these are so large that they were taking a majority of the time for the entire training loop! We discovered that they were achieving performance significantly below the peak throughput achievable on the A100 GPU, and guessed from NVIDIA's matmul documentation that 64-element alignment would yield better results. Indeed, padding these matmuls achieves nearly a 3x speedup! The underlying cause is that unaligned memory accesses significantly reduce efficiency. A deeper analysis can be found in this Twitter thread.
With this optimization we were able to further reduce training time from ~113 ms (using flash attention) to ~87 ms per batch.
Results
The figure below demonstrates the performance gained using Pytorch custom kernels. Here are the exact figures: | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
baseline (nanoGPT implementation): ~143ms
sdpa_math (generic): ~134ms (6.71% faster)
mem_efficient kernel: ~119ms (20.16% faster)
flash_attention kernel: ~113ms (26.54% faster)
flash_attention + padded vocab: ~87ms (64.37% faster)
All code was run on an 8 x NVIDIA Corporation A100 server with 80 GB HBM [A100 SXM4 80GB], and for the purpose of this experiment dropout was set to 0.
Figure 2: Using scaled dot product attention with custom kernels and torch.compile delivers significant speedups for training large language models, such as for nanoGPT shown here.
Enhancing Numerical Model Stability | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
Enhancing Numerical Model Stability
In addition to being faster, PyTorch's implementation offers increased numerical stability by avoiding loss of precision in many execution scenarios. There is a great explanation here, but essentially the PyTorch implementation scales the Query and Key matrices before multiplication, which is said to be more stable and avoid loss of precision. Because of the merged custom kernel architecture of SDPA, this scaling does not introduce additional overhead in the computation of the attention result. In comparison, an implementation from the individual computational components would require separate pre-scaling at additional cost. For an additional explanation, see Appendix A.
Improved Memory Consumption | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
Improved Memory Consumption
Yet another large advantage of using the torch SDPA kernels is the reduced memory footprint, which allows for the utilization of larger batch sizes. The following chart compares the best validation loss after one hour of training for both flash attention and the baseline implementations of causal attention. As can be seen, the maximum batch size achieved with the baseline causal attention implementation (on 8 x NVIDIA Corporation A100 server with 80 GB HBM) was 24, significantly less then the maximum achieved with flash attention, which was 39.
Figure 3: Using Flash Attention enables the usage of larger batch sizes, allowing users to achieve lower validation loss after one hour of training (smaller is better).
Conclusion | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
Conclusion
Accelerated PyTorch 2 Transformers were designed to make the training and production deployment of state-of-the-art transformer models affordable and integrated with PyTorch 2.0 model JIT compilation. The newly introduced PyTorch SDPA operator provides improved performance for training Transformer models and is particularly valuable for the expensive Large Language Model training. In this post we demonstrate a number of optimizations on the exemplary nanoGPT model including:
* Over 26% training speedup, when compared against the baseline with constant batch size
* An additional speedup achieved with padded vocabulary, bringing the total optimization to approximately 64% compared to the baseline
* Additional numerical stability
Appendix A: Analyzing Attention Numeric Stability | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
In this section we provide a more in depth explanation of the previously mentioned enhanced numerical stability which is gained by prescaling SDPA’s input vectors. The following is a simplified version of nanoGPT’s mathematical implementation of SDPA. The important thing to note here is that the query undergoes matrix multiplication without being scaled.
# nanoGPT implementation of SDPA
# notice q (our query vector) is not scaled !
att = (q @ k.transpose(-2, -1)) * (1.0 / math.sqrt(k.size(-1)))
att = att.masked_fill(self.bias[:,:,:T,:T] == 0, float('-inf'))
att = F.softmax(att, dim=-1)
# Dropout is set to 0, so we can safely ignore this line in the implementation# att = self.attn_dropout(att)
y_nanogpt = att @ v # (B, nh, T, T) x (B, nh, T, hs) -> (B, nh, T, hs)
The following is the equivalent mathematical implementation in torch’s scaled_dot_product_attention.
```
PyTorch implementation of SDPA
embed_size = q.size(-1)
scaling_factor = math.sqrt(math.sqrt(embed_size)) | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
scaling_factor = math.sqrt(math.sqrt(embed_size))
q = q / scaling_factor # notice q is scaled here !
same as above, but with scaling factor
att = q @ (k.transpose(-2, -1) / scaling_factor)
att = att.masked_fill(self.bias[:,:,:T,:T] == 0, float('-inf'))
att = F.softmax(att0, dim=-1)
Dropout is set to 0, so we can safely ignore this line in the implementation# att = self.attn_dropout(att)
y_scale_before = att @ v
Mathematically both approaches should be equivalent, however our experimentation shows that in practice we receive different results from each approach.
Using the approach above, we verified `y_scale_before` matches the expected output from using the `scaled_dot_product_attention `method while `y_nanogpt` does not.
The `torch.allclose` method was used to test equivalence. Specifically, we showed that:
y_sdpa = torch.nn.functional._scaled_dot_product_attention(
q,
k,
v,
attn_mask=self.bias[:,:,:T,:T] != 0,
dropout_p=0.0,
need_attn_weights=False,
is_causal=False,
) | https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
need_attn_weights=False,
is_causal=False,
)
torch.allclose(y_sdpa, y_nanogpt) # False, indicating fp issues
torch.allclose(y_sdpa, y_scale_before) # True, as expected
## Appendix B: Reproducing Experiment Results
Researchers seeking to reproduce these results should start with the following commit from Andrej’s nanoGPT repository - **<span style="text-decoration:underline;">b3c17c6c6a363357623f223aaa4a8b1e89d0a465</span>**. This commit was used as the baseline when measuring the per batch speed improvements. For results which include padded vocabulary optimizations (which yielded the most significant improvements to batch speed), use the following commit - **<span style="text-decoration:underline;">77e7e04c2657846ddf30c1ca2dd9f7cbb93ddeab</span>**. From either checkout, selecting kernels for experimentation is made trivial with the use of the [torch.backends](https://pytorch.org/docs/stable/backends.html) API.
The desired kernel can be selected via a context manager:
| https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
with torch.backends.cuda.sdp_kernel (
enable_math = False,
enable_flash = False,
enable_mem_efficient = True
):
train(model)
| https://pytorch.org/blog/accelerating-large-language-models/ | pytorch blogs |
layout: blog_detail
title: "Introducing Hidet: A Deep Learning Compiler for Efficient Model Serving"
author: Team Hidet
Hidet is a powerful deep learning compiler that simplifies the process of implementing high-performing deep learning operators on modern accelerators (e.g., NVIDIA GPUs). With the new feature of torch.compile(...) in PyTorch 2.0, integrating a novel compiler into PyTorch is easier than ever - Hidet now can be used as a torch.compile(...) backend to accelerate PyTorch models, making it an attractive option for PyTorch users who want to improve the inference performance of their models, especially for those who also need to implement extremely optimized custom operators.
Using Hidet to Compile A PyTorch Model
To use Hidet in PyTorch, you need to first install the hidet package via pip:
pip install hidet
| https://pytorch.org/blog/introducing-hidet/ | pytorch blogs |
pip install hidet
Hidet is integrated with PyTorch as a torch.compile(...) backend following the Custom Backends tutorial. You can specify hidet as the backend when you compile a model. (Note: requires PyTorch version 2.0+):
torch.compile(..., backend='hidet')
| https://pytorch.org/blog/introducing-hidet/ | pytorch blogs |
torch.compile(..., backend='hidet')
Hidet converts the given PyTorch model in the torch.fx.Graph format into its internal graph representation, and conducts a series of optimizations. Hidet provides a few options to configure the optimizations. For example, we can use hidet.torch.dynamo_config.use_tensor_core(True) to allow Hidet to generate CUDA kernels that leverage the Tensor Cores on NVIDIA GPUs, and use hidet.torch.dynamo_config.search_space(2) to allow Hidet to search for the best operator schedule specific for your hardware and input sizes. More configurations can be found in Hidet’s documentation.
Here's a complete example of how to use Hidet to compile and optimize a pre-trained ResNet50 model from torchvision:
```
import hidet
import torch
Load a pre-trained ResNet50 model
x = torch.randn(1, 3, 224, 224, device='cuda').half()
model = torch.hub.load( | https://pytorch.org/blog/introducing-hidet/ | pytorch blogs |
model = torch.hub.load(
'pytorch/vision:v0.6.0', 'resnet50', pretrained=True
).cuda().half().eval()
Configure hidet to use tensor core and enable tuning
hidet.torch.dynamo_config.use_tensor_core(True)
hidet.torch.dynamo_config.search_space(2)
Compile the model using Hidet
model_opt = torch.compile(model, backend='hidet')
Check correctness
torch.testing.assert_close(actual=model_opt(x), expected=model(x), rtol=1e-2, atol=1e-2)
Benchmark
from hidet.utils import benchmark_func
print('eager: {:2f}'.format(benchmark_func(lambda: model(x))))
print('hidet: {:2f}'.format(benchmark_func(lambda: model_opt(x))))
``` | https://pytorch.org/blog/introducing-hidet/ | pytorch blogs |
We encourage you to try out the above script on your own NVIDIA GPU(s)! If you run this script on an `aws.g5.2xlarge` instance, you would get the result shown in the following figure. Hidet achieves the speedup because it could automatically fuse multiple operators, tune operator schedules, and use CUDA Graph to reduce framework-level overhead. More results can be found in the [ASPLOS’23 publication of Hidet](https://dl.acm.org/doi/10.1145/3575693.3575702) and our [performance tracking](https://github.com/hidet-org/hidet/issues/154)
{:style="max-height:800px; width:100%"}
## Using Hidet Script to Write Custom Operators
Hidet Script is one approach to implement tensor operators in Python. The following example shows how to implement a naive matrix multiplication using Hidet Script and integrate it as a PyTorch operator.
import torch
import hidet
def matmul(m_size, n_size, k_size):
from hidet.lang import f32, attr | https://pytorch.org/blog/introducing-hidet/ | pytorch blogs |
from hidet.lang import f32, attr
from hidet.lang.cuda import threadIdx, blockIdx, blockDim
with hidet.script_module() as script_module:
@hidet.script
def matmul(
a: f32[m_size, k_size],
b: f32[k_size, n_size],
c: f32[m_size, n_size]
):
attr.cuda_grid_dim = ((m_size + 31) // 32, (n_size + 31) // 32)
attr.cuda_block_dim = (32, 32)
i = threadIdx.x + blockIdx.x * blockDim.x
j = threadIdx.y + blockIdx.y * blockDim.y
if i < m_size and j < n_size:
c[i, j] = 0.0
for k in range(k_size):
c[i, j] += a[i, k] * b[k, j]
ir_module = script_module.ir_module()
func = hidet.driver.build_ir_module(ir_module)
return func
class NaiveMatmul(torch.autograd.Function):
@staticmethod
def forward(ctx, a, b):
m, k = a.shape
k, n = b.shape
c = torch.empty([m, n], dtype=a.dtype, device=a.device) | https://pytorch.org/blog/introducing-hidet/ | pytorch blogs |
func = matmul(m, n, k)
func(a, b, c)
return c
a = torch.randn([3, 4], device='cuda')
b = torch.randn([4, 5], device='cuda')
c = NaiveMatmul.apply(a, b)
cc = torch.matmul(a, b)
torch.testing.assert_close(c, cc)
```
More optimizations can be applied, see the example in our documentation to learn more. | https://pytorch.org/blog/introducing-hidet/ | pytorch blogs |
Hidet Script vs. Triton: Triton greatly simplifies the CUDA programming by introducing the tile-based programming model where the parallel execution unit is thread blocks instead of threads. However, this simplification also prevents the tensor program developers from manipulating the fine-grained computation and memory resources (e.g., warps, shared memory) in their preferred ways. It would be challenging to implement an optimization that requires fine-grained control of these resources using Triton if it has not been implemented by the Triton compiler itself. Hidet Script, on the other hand, simplifies tensor programming while still enabling users to implement their own optimizations with extensive flexibility. It's worth noting that the more granular control of Hidet Script also brings added complexity compared to Triton.
More about Hidet | https://pytorch.org/blog/introducing-hidet/ | pytorch blogs |
More about Hidet
Hidet originates from a research project led by the EcoSystem lab at the University of Toronto (UofT) and AWS. The authors propose a new way, named the task-mapping programming paradigm, to construct tensor programs. It aims to simplify the tensor programming without sacrificing any optimization opportunity. Now, Hidet is an open-source project, jointly supported by CentML and the EcoSystem lab, that aims to provide an efficient solution to end-to-end inference on modern accelerators (e.g., NVIDIA GPUs).
Additional Resources
GitHub Repository: https://github.com/hidet-org/hidet
Hidet’s Documentation: https://docs.hidet.org
ASPLOS ’23 Publication: https://dl.acm.org/doi/10.1145/3575693.3575702
ASPLOS ’23 Tutorial: https://centml.github.io/asplos23-tutorial/
| https://pytorch.org/blog/introducing-hidet/ | pytorch blogs |
Acknowledgement
We would like to thank Jerry Park, Mark Saroufim, Jason Liang and Helen Suk for their valuable help on preparing the blog post and feedback on the text. We also would like to thank Nikita Shulga, Jason Ansel, and Dmytro Dzhulgakov for reviewing and improving our PR https://github.com/pytorch/pytorch/pull/93873 on the 3rd-party dynamo backend registration. | https://pytorch.org/blog/introducing-hidet/ | pytorch blogs |
layout: blog_detail
title: "PyTorch, a year in...."
author: "The PyTorch Team"
date: 2018-01-19 12:00:00 -0500
redirect_from: /2018/01/19/a-year-in.html
Today marks 1 year since PyTorch was released publicly. It's been a wild ride — our quest to build a flexible deep learning research platform. Over the last year, we've seen an amazing community of people using, contributing to and evangelizing PyTorch — thank you for the love.
Looking back, we wanted to summarize PyTorch over the past year: the progress, the news and highlights from the community.
Community
We've been blessed with a strong organic community of researchers and engineers who fell in love with PyTorch. The core team has engineers and researchers from multiple countries, companies and universities, and we couldn't have made PyTorch what it is without each contribution.
Research papers, packages and Github | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Research papers, packages and Github
Within days of release, users from the community started to implement their favorite research papers in PyTorch and release the code on Github. Open-source code is a primary and essential tool for researchers today.
Folks came together to create torchtext, torchvision and torchaudio packages to help facilitate and democratize research in different domains.
The first community package based on PyTorch came from Brandon Amos, titled Block, and helped with easier manipulation of block matrices. The Locus Lab at CMU subsequently went on to publish PyTorch packages and implementations for most of their research. The first research paper code came from Sergey Zagoruyko titled Paying more attention to attention. | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Jun-Yan Zhu, Taesung Park, Phillip Isola, Alyosha Efros and team from U.C.Berkeley released the hugely popular Cycle-GAN and pix2pix which does image to image transforms.
The researchers at HarvardNLP and Systran started developing and improving OpenNMT in PyTorch, seeded by initial reimplementation of the [Lua]Torch code from Adam Lerer at Facebook.
The MagicPony team at Twitter contributed implementations of their Super-resolution work early on into PyTorch's examples. | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Salesforce Research released several packages, including their highlight release of PyTorch-QRNN, a type of RNN that is 2x to 17x faster than standard LSTMs optimized by CuDNN. James Bradbury and team form one of the most active and engaging forces in the PyTorch community.
We're releasing @PyTorch-QRNN, 2-17x faster than NVIDIA's cuDNN LSTM.Speed thanks to 50 lines of CUDA via CuPy.https://t.co/KaWhN4yDZd pic.twitter.com/yoLYj3pMI0— Smerity (@Smerity) October 9, 2017
| https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Researchers from Uber, Northeastern and Stanford came together to form an active probabilistic programming community around their packages Pyro and ProbTorch. They are actively developing the torch.distributions core package. This community is so active and fast-moving, we had our first pytorch-probabilistic-programming meetup at NIPS 2017 with Fritz Obermeyer, Noah Goodman, Jan-Willem van de Meent, Brooks Paige, Dustin Tran and 22 additional attendees discussing how to make the world bayesian.
| https://pytorch.org/blog/a-year-in/ | pytorch blogs |
NVIDIA Researchers released three high-quality repositories that implemented pix2pix-HD, Sentiment Neuron and FlowNet2 papers. Their analysis of scalability of different Data Parallel models in PyTorch was helpful to the community.
The Allen Institute for AI released AllenNLP which includes several state-of-the-art models in NLP — reference implementations and easy to use web demos for standard NLP tasks.
| https://pytorch.org/blog/a-year-in/ | pytorch blogs |
We also had our first Kaggle winning team grt123 in July. They won the DataScience Bowl 2017 on Lung Cancer detection and subsequently released their PyTorch implementations.
On the visualization front, Tzu-Wei Huang implemented a TensorBoard-PyTorch plugin and Facebook AI Research released PyTorch compatibility for their visdom visualization package.
Lastly, Facebook AI Research released several projects such as ParlAI, fairseq-py, VoiceLoop and FaderNetworks that implemented cutting-edge models and interfaced datasets in multiple domains. | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
There are countless good projects that we haven't highlighted for the lack of space, you can find a curated list here.
We would also like to give a huge shout-out to folks who actively help others out on the Forums, especially ptrblck, jpeg729, QuantScientist, albanD, Thomas Viehmann and chenyuntc. You are providing an invaluable service, thank you so much!
Metrics
In terms of sheer numbers,
* 87,769 lines of Python code on github that import torch
* 3,983 repositories on Github that mention PyTorch in their name or description | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
More than half a million downloads of PyTorch binaries. 651,916 to be precise.
5,400 users wrote 21,500 posts discussing 5,200 topics on our forums discuss.pytorch.org (http://discuss.pytorch.org/)
131 mentions of PyTorch on Reddit's /r/machinelearning since the day of release. In the same period, TensorFlow was mentioned 255 times.
Research Metrics
PyTorch is a research-focused framework. So one of the metrics of interest is to see the usage of PyTorch in machine learning research papers.
* In the recent ICLR2018 conference submissions, PyTorch was mentioned in 87 papers, compared to TensorFlow at 228 papers, Keras at 42 papers, Theano and Matlab at 32 papers.
* Monthly arxiv.org mentions for frameworks had PyTorch at 72 mentions, with TensorFlow at 273 mentions, Keras at 100 mentions, Caffe at 94 mentions and Theano at 53 mentions.
Courses, Tutorials and Books | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Courses, Tutorials and Books
When we released PyTorch, we had good API documentation, but our tutorials were limited to a few ipython notebooks — helpful, but not good enough.
Sasank Chilamkurthy took it upon himself to revamp the tutorials into the beautiful website that it is today.
Sean Robertson and Justin Johnson wrote great new tutorials — in NLP, and to learn by example. Yunjey Choi wrote a beautiful tutorial where most models were implemented in 30 lines or less.
Each new tutorial helped users find their way faster, with different approaches to learning. | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Goku Mohandas and Delip Rao switched the code content of their book-in-progress to use PyTorch.
We've seen quite a few university machine learning courses being taught with PyTorch as the primary tool, such as Harvard's CS287. Taking it one step further and democratizing learning, we had three online courses pop up that teach using PyTorch.
- Fast.ai's “Deep Learning for Coders” is a popular online course. In September, Jeremy and Rachel announced that the next fast.ai courses will be nearly entirely based on PyTorch.
- Ritchie Ng, a researcher with ties to NUS Singapore and Tsinghua released a Udemy course titled Practical Deep Learning with PyTorch. | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Sung Kim from HKUST released an online course on Youtube that was aimed towards a general audience, titled: “PyTorch Zero to All”.
Engineering
Over the last year we implemented multiple features, improved performance across the board and fixed lots of bugs. A full list of the work we've done is found in our release notes.
Here are highlights from our work over the last year:
Higher-order gradients
With the release of several papers that implement penalties of gradients and with ongoing research in 2nd order gradient methods, this was an essential and sought-after feature. In August, we implemented a generalized interface that can take n-th order derivatives and increased the coverage of functions that support higher-order gradients over time, such that at the moment of writing almost all ops support this.
Distributed PyTorch | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Distributed PyTorch
In August, we released a small distributed package that followed the highly popular MPI-collective approach. The package has multiple backends such as TCP, MPI, Gloo and NCCL2 to support various types of CPU/GPU collective operations and use-cases, and integrates distributed technologies such as Infiniband and RoCE. Distributed is hard, and we had bugs in the initial iteration. Over subsequent releases, we made the package more stable and improved performance.
Closer to NumPy
One of the biggest demands from users were NumPy features that they were familiar with. Features such as Broadcasting and Advanced Indexing are convenient and save users a lot of verbosity. We implemented these features and started to align our API to be closer to NumPy. Over time, we expect to get closer and closer to NumPy's API where appropriate.
Sparse Tensors | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Sparse Tensors
In March, we released a small package supporting sparse Tensors and in May we released CUDA support for the sparse package. The package is small and limited in functionality, and is used for implementing Sparse Embeddings and commonly used sparse paradigms in deep learning. This package is still small in scope and there's demand to expand it — if you are interested in working on expanding the sparse package, reach out to us on our Discussion Boards
Performance
Performance is always an ongoing battle, especially for PyTorch which is a dynamic framework that wants to maximize flexibility. Over the last year, we've improved performance across board, from our core Tensor library to the neural network operators, writing faster micro-optimized across board.
* We've added specialized AVX and AVX2 intrinsics for Tensor operations
* Wrote faster GPU kernels for frequent workloads like concatenation and Softmax (among many other things) | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Rewrote the code for several neural network operators (too many to list), but notably nn.Embedding and group convolutions.
Reducing framework overhead by 10x across board
Since PyTorch is a dynamic graph framework, we create a new graph on the fly at every iteration of a training loop. Hence, the framework overhead has to be low, or the workload has to be large enough that the framework overhead is hidden. In August, the authors of DyNet (Graham Neubig and team) showcased that it's much faster than PyTorch on small NLP models. This was an interesting challenge, we didn't realize that models of those sizes were being trained. In a multi-month (and ongoing) effort, we embarked upon a significant rewrite of PyTorch internals that reduced the framework overhead from more than 10 microseconds per operator execution to as little as 1 microsecond.
ATen
| https://pytorch.org/blog/a-year-in/ | pytorch blogs |
ATen
As we embarked upon a redesign of the PyTorch internals, we built the ATen C++11 library that now powers all of the PyTorch backend. ATen has an API that mirrors PyTorch's Python API, which makes it a convenient C++ library for Tensor computation. ATen can be built and used independently of PyTorch.
Exporting models to production — ONNX Support and the JIT compiler
One of the common requests we've received was to export PyTorch models to another framework. Users engaged in a rapid research cycle in PyTorch and when they were done, they wanted to ship it to larger projects with C++ only requirements.
With this in mind, we built a tracer for PyTorch — which can export PyTorch models into an intermediate representation. | https://pytorch.org/blog/a-year-in/ | pytorch blogs |
The subsequent trace can be either used to run the current PyTorch model more efficiently (by running optimization passes on it), or be converted to the ONNX format to be shipped to other frameworks such as Caffe2, MXNet, TensorFlow and others or directly to the hardware accelerated libraries like CoreML or TensorRT. Over the next year, you will hear more about the JIT compiler for performance improvements.
Users being funny :)
Our users express their support in funny ways, made us laugh, thanks for this :)
I've been using PyTorch a few months now and I've never felt better. I have more energy. My skin is clearer. My eye sight has improved.— Andrej Karpathy (@karpathy) May 26, 2017
| https://pytorch.org/blog/a-year-in/ | pytorch blogs |
Talk to your doctor to find out if PyTorch is right for you.— Sean Robertson (@sprobertson) May 26, 2017
PyTorch gave me so much life that my skin got cleared, my grades are up, my bills are paid and my crops are watered.— Adam Will ð️ð (@adam_will_do_it) May 26, 2017
| https://pytorch.org/blog/a-year-in/ | pytorch blogs |
So have I! But my hair is also shiner and I've lost weight. @PyTorch for the win. https://t.co/qgU4oIOB4K— Mariya (@thinkmariya) May 26, 2017
| https://pytorch.org/blog/a-year-in/ | pytorch blogs |
layout: blog_detail
title: "Out of the box acceleration and memory savings of 🤗 decoder models with PyTorch 2.0"
author: Felix Marty, Younes Belkada, Hamid Shojanazeri
As part of PyTorch 2.0 release, an accelerated implementation of the attention mechanism as part of the “Better Transformer” project (and known in PyTorch as Accelerated Transformers) has been added natively into PyTorch as torch.nn.functional.scaled_dot_product_attention. This implementation leverages fused kernels from FlashAttention and Memory-efficient attention, and supports both training and inference.
We also release a notebook showcasing an example of this integration here | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
After seeing 20-30% speedups at inference for diffusion models, we went ahead and implemented an integration with 🤗 Transformers models through the 🤗 Optimum library. Similar to the previous integration for encoder models, the integration replaces modules from Transformers with efficient implementations that use torch.nn.functional.scaled_dot_product_attention. The usage is as follow:
```
from optimum.bettertransformer import BetterTransformer
from transformers import AutoModelForCausalLM
with torch.device(“cuda”):
model = AutoModelForCausalLM.from_pretrained(“gpt2-large”, torch_dtype=torch.float16)
model = BetterTransformer.transform(model)
do your inference or training here
if training and want to save the model
model = BetterTransformer.reverse(model) | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
model = BetterTransformer.reverse(model)
model.save_pretrained(“fine_tuned_model”)
model.push_to_hub(“fine_tuned_model”)
Summarizing our findings below about `torch.nn.functional.scaled_dot_product_attention`:
* It is most useful to fit larger models, sequence length, or batch size to train on a given hardware.
* Memory footprint savings on GPU during training range from 20% to 110%+.
* Speedups during training range from 10% to 70%.
* Speedups during inference range from 5% to 20%.
* Standalone, for small head dimensions, `scaled_dot_product_attention` speedups go up to 3x, memory savings go as high as 40x (depending on the sequence length).
You may be surprised by the wide range of memory savings and speedups. In this blog post, we discuss our benchmarks, where this feature shines and upcoming improvements in future PyTorch releases.
_In the next release of transformers you will just need to install the proper version of optimum and run:_
model = model.to_bettertransformer()
``` | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
model = model.to_bettertransformer()
To convert your model using the BetterTransformer API. You can already try this feature out by installing transformers from source.
Benchmark and usage with 🤗 Transformers
torch.nn.functional.scaled_dot_product_attention is usable with any architecture that uses standard attention, and namely replaces the boiler-plate code:
# native scaled_dot_product_attention is equivalent to the following:
def eager_sdpa(query, key, value, attn_mask, dropout_p, is_causal, scale):
scale_factor = 1 / math.sqrt(Q.size(-1)) if scale is None else scale
attn_mask = torch.ones(L, S, dtype=torch.bool).tril(diagonal=0) if is_causal else attn_mask
attn_mask = attn_mask.masked_fill(not attn_mask, -float('inf')) if attn_mask.dtype==torch.bool else attn_mask
attn_weight = torch.softmax((Q @ K.transpose(-2, -1) * scale_factor) + attn_mask, dim=-1)
attn_weight = torch.dropout(attn_weight, dropout_p)
return attn_weight @ V
| https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
return attn_weight @ V
```
In the 🤗 Optimum integration with Transformers models, the following architectures are supported for now: gpt2, gpt-neo, gpt-neox, gptj, t5, bart, codegen, pegasus, opt, LLaMA, blenderbot, m2m100. You can expect this list to be extended in the near future!
To validate the benefits from the native scaled dot-product attention, we ran inference and training benchmarks, whose results are presented below.
Inference benchmark on a single A10G GPU, AWS g5.4xlarge instance
Training benchmark on a single A10G GPU, AWS g5.4xlarge instance
| https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
Training benchmark on a single A100-SXM4-80GB, Nvidia DGX
Out of this benchmark, the most interesting finding is that native SDPA allows for the usage of longer sequence lengths and batch sizes without running into out of memory issues. Moreover, up to 20% speedups can be seen during inference, and even larger during training.
As seen on the training benchmarks, it appears that smaller head dimension brings higher speedups and memory savings, which we will discuss in the following section.
The implementation supports multi-GPU settings as well, thanks to 🤗 Accelerate library by passing device_map=”auto” to the from_pretrained method. Here are some results for training on two A100-SXM4-80GB. | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
Training benchmark on two A100-SXM4-80GB, Nvidia DGX, using 🤗 Accelerate library for distributed training
Note that some kernels support only the sm_80 compute capability (which is the one from A100 GPUs), which limits usability on a wide range of hardware, notably if the head dimension is not a power of two. For example, as of PyTorch 2.0.0 during training, opt-2.7b (headim=80) and gpt-neox-20b (headdim=96) can not dispatch to a kernel using flash attention, unless run on an A100 GPU. Better kernels may be developed in the future: https://github.com/pytorch/pytorch/issues/98140#issuecomment-1518101895
Flash Attention, Memory-efficient attention & math differences | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
The native scaled_dot_product_attention relies on three possible backend implementations: flash attention, memory-efficient attention, and the so-called math implementation which provides a hardware-neutral fallback for all PyTorch platforms.
When fused kernels are available for a given problem size, flash-attention or memory-efficient attention will be used, effectively allowing for a lower memory footprint, as in the memory-efficient attention case O(N) memory allocations are done on the GPU global memory instead of the classic O(N^2) for the traditional eager attention implementation. With flash attention, a reduced number of memory accesses (read and writes) is expected, hence both giving speedups and memory savings. | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
The “math” implementation is simply an implementation using the PyTorch’s C++ API. Interesting to note in this implementation is that the query and key tensors are scaled individually for numerical stability, thus launching two aten::div operations instead of possibly only one in an eager implementation that does not contain this optimization for numerical stability.
Head dimension influence on speedups, memory savings | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
Benchmarking torch.nn.functional.scaled_dot_product_attention, we notice a decrease in the speedup / memory gains as the head dimension increases. This is an issue for some architectures like EleutherAI/gpt-neo-2.7B, that has a relatively large head dimension of 128, or EleutherAI/gpt-j-6B (and derived models as PygmalionAI/pygmalion-6b) that has a head dimension of 256 (that actually currently do not dispatch on fused kernels as the head dimension is too large).
This trend can be seen in the figures below, where torch.nn.scaled_dot_production is benchmarked standalone versus the above eager implementation. Moreover, we use the torch.backends.cuda.sdp_kernel context manager to force the usage of respectively math, flash attention, and memory-efficient attention implementation.
| https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
Using memory-efficient attention SDP kernel (forward-only), A100
Using math (without dropout), A100
Using flash attention SDP kernel (without dropout), A100
Using memory-efficient attention SDP kernel (without dropout), A100
| https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
We see that for the same problem size, be it for inference-only or training, the speedup decreases with higher head dimension, e.g. from 3.4x for headdim=8 to 1.01x for headdim=128 using flash attention kernel.
The reduced memory saving is expected with larger head dimensions. Recall the standard attention computation:
Due to the intermediate computations, the global memory footprint is 2 * N * N + N * d in this standard step by step computation. Memory-efficient attention proposes to iteratively update the softmax renormalization constant and moving its computation at the very end, allowing for only a constant output memory allocation N * d.
Thus, the memory saving ratio is 2 * N / d + 1, which decreases with larger head dimension. | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
In flash attention, the tradeoff is between the head dimension d and the shared memory size M of a GPU streaming multiprocessor, with a total number of memory accesses of O(N² * d²/M). Thus, the memory accesses scale quadratically in the head dimension, contrary to the standard attention that scales linearly. The reason is that in flash attention, for larger head dimension d, the key and value K, V need to be split into more blocks to fit into shared memory, and in turn each block needs to load the full query Q and output O.
Thus, the highest speedups for flash attention are in a regime where the ratio d² / M is small enough.
Current limitations as of PyTorch 2.0.0
Absence of a scale argument
As of PyTorch 2.0.0, torch.nn.functional.scaled_dot_product_attention has no scale argument and uses the default square root of the hidden size sqrt(d_k).
| https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
However, some architectures as OPT or T5 do not use a scaling in the attention, which as of Pytorch 2.0.0 forces it to artificially rescale before the scaled_dot_product_attention call. This introduces an unnecessary overhead, as an additional multiplication is necessary, on top of unneeded divisions in the attention.
A fix for this issue has been merged in PyTorch repository.
Support of flash attention / memory-efficient attention with custom mask
As of PyTorch 2.0.0, when passing a custom attention mask, flash attention and memory-efficient attention can not be used. In this case, scaled_dot_product_attention automatically dispatches to the C++ implementation. | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
However, as we have seen, some architectures require a custom attention mask, as T5 that uses positional bias. Moreover, in the case of a batch size larger than one where some inputs may be padded, a custom attention mask also needs to be passed. For this latter case, an alternative would be to use NestedTensor, which SDPA supports.
This limited support for custom masks thus limits the benefits from SDPA in these specific cases, although we can hope for an extended support in the future. | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
Note that xformers, from which PyTorch’s SDPA partially takes inspiration, currently supports arbitrary attention masks: https://github.com/facebookresearch/xformers/blob/658ebab39545f180a6075385b3897921623d6c3b/xformers/ops/fmha/cutlass.py#L147-L156 . HazyResearch implementation of flash attention also supports an equivalent implementation of padding, as a cumulative sequence length array is used along with packed query/key/values - similar in essence to NestedTensor.
In conclusion
Using torch.nn.functional.scaled_dot_product_attention is a free-lunch optimization, both making your code more readable, uses less memory, and is in most common cases faster.
Although the implementation in PyTorch 2.0.0 has still minor limitations, inference and training already massively benefit from SDPA in most cases. We encourage you to use this native implementation be it to train or deploy your PyTorch models, and for 🤗 Transformers models as a one-line transformation! | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
In the future, we would like to adapt the API to enable users to use SDPA in encoder-based models as well.
We thank Benjamin Lefaudeux, Daniel Haziza and Francisco Massa for their advice on the head dimension influence, as well as Michael Gschwind, Christian Puhrsch and Driss Guessous for their feedback on the blog post!
Benchmark reproduction
The benchmark presented in this post was done using torch==2.0.0, transformers==4.27.4, accelerate==0.18.0 and optimum==1.8.0.
The benchmarks can be easily reproduced using the scripts for inference, training for 🤗 Transformers models, and standalone SDPA. | https://pytorch.org/blog/out-of-the-box-acceleration/ | pytorch blogs |
layout: blog_detail
title: 'Announcing the Winners of the 2020 Global PyTorch Summer Hackathon'
author: Team PyTorch
More than 2,500 participants in this year’s Global PyTorch Summer Hackathon pushed the envelope to create unique new tools and applications for PyTorch developers and researchers.
Notice: None of the projects submitted to the hackathon are associated with or offered by Facebook, Inc.
This year’s projects fell into three categories:
* PyTorch Developer Tools: a tool or library for improving productivity and efficiency for PyTorch researchers and developers.
* Web/Mobile Applications Powered by PyTorch:** a web or mobile interface and/or an embedded device built using PyTorch. | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
PyTorch Responsible AI Development Tools: a tool, library, or web/mobile app to support researchers and developers in creating responsible AI that factors in fairness, security, privacy, and more throughout its entire development process.
The virtual hackathon ran from June 22 to August 25, with more than 2,500 registered participants, representing 114 countries from Republic of Azerbaijan, to Zimbabwe, to Japan, submitting a total of 106 projects. Entrants were judged on their idea’s quality, originality, potential impact, and how well they implemented it.
Meet the winners of each category below.
PyTorch Developer Tools
1st place - DeMask | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
DeMask is an end-to-end model for enhancing speech while wearing face masks — offering a clear benefit during times when face masks are mandatory in many spaces and for workers who wear face masks on the job. Built with Asteroid, a PyTorch-based audio source separation toolkit, DeMask is trained to recognize distortions in speech created by the muffling from face masks and to adjust the speech to make it sound clearer.
This submission stood out in particular because it represents both a high-quality idea and an implementation that can be reproduced by other researchers.
Here is an example on how to train a speech separation model in less than 20 lines:
```python
from torch import optim
from pytorch_lightning import Trainer
from asteroid import ConvTasNet
from asteroid.losses import PITLossWrapper
from asteroid.data import LibriMix
from asteroid.engine import System
train_loader, val_loader = LibriMix.loaders_from_mini(task='sep_clean', batch_size=4) | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
model = ConvTasNet(n_src=2)
optimizer = optim.Adam(model.parameters(), lr=1e-3)
loss = PITLossWrapper(
lambda x, y: (x - y).pow(2).mean(-1), # MSE
pit_from="pw_pt", # Point in the pairwise matrix.
)
system = System(model, optimizer, loss, train_loader, val_loader)
trainer = Trainer(fast_dev_run=True)
trainer.fit(system)
```
2nd place - carefree-learn
A PyTorch-based automated machine learning (AutoML) solution, carefree-learn provides high-level APIs to make training models using tabular data sets simpler. It features an interface similar to scikit-learn and functions as an end-to-end end pipeline for tabular data sets. It automatically detects feature column types and redundant feature columns, imputes missing values, encodes string columns and categorical columns, and preprocesses numerical columns, among other features.
3rd Place - TorchExpo | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
TorchExpo is a collection of models and extensions that simplifies taking PyTorch from research to production in mobile devices. This library is more than a web and mobile application, and also comes with a Python library. The Python library is available via pip install and it helps researchers convert a state-of-the-art model in TorchScript and ONNX format in just one line. Detailed docs are available here.
Web/Mobile Applications Powered by PyTorch
1st place - Q&Aid | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
Q&Aid is a conceptual health-care chatbot aimed at making health-care diagnoses and facilitating communication between patients and doctors. It relies on a series of machine learning models to filter, label, and answer medical questions, based on a medical image and/or questions in text provided by a patient. The transcripts from the chat app then can be forwarded to the local hospitals and the patient will be contacted by one of them to make an appointment to determine proper diagnosis and care. The team hopes that this concept application helps hospitals to work with patients more efficiently and provide proper care.
2nd place - Rasoee | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
Rasoee is an application that can take images as input and output the name of the dish. It also lists the ingredients and recipe, along with the link to the original recipe online. Additionally, users can choose a cuisine from the list of cuisines in the drop menu, and describe the taste and/or method of preparation in text. Then the application will return matching dishes from the list of 308 identifiable dishes. The team has put a significant amount of effort gathering and cleaning various datasets to build more accurate and comprehensive models. You can check out the application here.
3rd place - Rexana the Robot — PyTorch | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
Rexana is an AI voice assistant meant to lay the foundation for a physical robot that can complete basic tasks around the house. The system is capable of autonomous navigation (knowing its position around the house relative to landmarks), recognizing voice commands, and object detection and recognition — meaning it can be commanded to perform various household tasks (e.g., "Rexana, water the potted plant in the lounge room.”). Rexana can be controlled remotely via a mobile device, and the robot itself features customizable hands (magnets, grippers, etc.) for taking on different jobs.
PyTorch Responsible AI Development Tools
1st place: FairTorch | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
FairTorch is a fairness library for PyTorch. It lets developers add constraints to their models to equalize metrics across subgroups by simply adding a few lines of code. Model builders can choose a metric definition of fairness for their context, and enforce it at time of training. The library offers a suite of metrics that measure an AI system’s performance among subgroups, and can apply to high-stakes examples where decision-making algorithms are deployed, such as hiring, school admissions, and banking.
2nd place: Fluence | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
Fluence is a PyTorch-based deep learning library for language research. It specifically addresses the large compute demands of natural language processing (NLP) research. Fluence aims to provide low-resource and computationally efficient algorithms for NLP, giving researchers algorithms that can enhance current NLP methods or help discover where current methods fall short.
3rd place: Causing: CAUSal INterpretation using Graphs | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
Causing (CAUSal INterpretation using Graphs) is a multivariate graphic analysis tool for bringing transparency to neural networks. It explains causality and helps researchers and developers interpret the causal effects of a given equation system to ensure fairness. Developers can input data and a model describing the dependencies between the variables within the data set into Causing, and Causing will output a colored graph of quantified effects acting between the model’s variables. In addition, it also allows developers to estimate these effects to validate whether data fits a model.
Thank you,
The PyTorch team | https://pytorch.org/blog/announcing-the-winners-of-the-2020-global-pytorch-summer-hackathon/ | pytorch blogs |
layout: blog_detail
title: "Get Started with PyTorch 2.0 Summary and Overview"
author: Team PyTorch
featured-img: "assets/images/Pytorch_2_0_Animation_AdobeExpress.gif"
Introducing PyTorch 2.0, our first steps toward the next generation 2-series release of PyTorch. Over the last few years we have innovated and iterated from PyTorch 1.0 to the most recent 1.13 and moved to the newly formed PyTorch Foundation, part of the Linux Foundation.
To complement the PyTorch 2.0 announcement and conference, we have also posted a comprehensive introduction and technical overview within the Get Started menu at https://pytorch.org/get-started/pytorch-2.0.
We also wanted to ensure you had all the information to quickly leverage PyTorch 2.0 in your models so we added the technical requirements, tutorial, user experience, Hugging Face benchmarks and FAQs to get you started today! | https://pytorch.org/blog/getting-started-with-pytorch-2.0/ | pytorch blogs |
Finally we are launching a new “Ask the Engineers: 2.0 Live Q&A” series that allows you to go deeper on a range of topics with PyTorch subject matter experts. We hope this content is helpful for the entire community and level of users/contributors.
https://pytorch.org/get-started/pytorch-2.0 | https://pytorch.org/blog/getting-started-with-pytorch-2.0/ | pytorch blogs |
layout: blog_detail
title: 'An Overview of the PyTorch Mobile Demo Apps'
author: Jeff Tang and Mark Saroufim
featured-img: 'assets/images/android-demo-app.png'
date: 2021-06-18 12:00:00 -0500
PyTorch Mobile provides a runtime environment to execute state-of-the-art machine learning models on mobile devices. Latency is reduced, privacy preserved, and models can run on mobile devices anytime, anywhere.
In this blog post, we provide a quick overview of 10 currently available PyTorch Mobile powered demo apps running various state-of-the-art PyTorch 1.9 machine learning models spanning images, video, audio and text.
It’s never been easier to deploy a state-of-the-art ML model to a phone. You don’t need any domain knowledge in Machine Learning and we hope one of the below examples resonates enough with you to be the starting point for your next project.
Computer Vision
Image Classification | https://pytorch.org/blog/mobile-demo-apps-overview/ | pytorch blogs |
Computer Vision
Image Classification
This app demonstrates how to use PyTorch C++ libraries on iOS and Android to classify a static image with the MobileNetv2/3 model.
iOS #1 iOS #2 Android #1 Android #2
iOS Android
Live Image Classification
This app demonstrates how to run a quantized MobileNetV2 and Resnet18 models to classify images in real time with an iOS and Android device camera. | https://pytorch.org/blog/mobile-demo-apps-overview/ | pytorch blogs |
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