[tab] train_lam.py (python)
from dataclasses import dataclass, field
import os
from typing import cast

import einops
from jax.sharding import Mesh, PartitionSpec, NamedSharding
from jax.experimental.mesh_utils import create_device_mesh
import optax
import orbax.checkpoint as ocp
import numpy as np
import dm_pix as pix
import jax
import jax.numpy as jnp
import tyro
import wandb
import grain
import flax.nnx as nnx

from models.lam import LatentActionModel
from utils.dataloader import create_dataloader_iterator
from utils.lr_utils import get_lr_schedule
from utils.parameter_utils import count_parameters_by_component


@dataclass
class Args:
    # Experiment
    num_steps: int = 200_000
    seed: int = 0
    seq_len: int = 16
    image_channels: int = 3
    image_height: int = 90
    image_width: int = 160
    data_dir: str = ""
    save_ckpt: bool = False
    restore_ckpt: bool = False
    # Optimization
    batch_size: int = 36
    vq_beta: float = 0.25
    init_lr: float = 0.0
    max_lr: float = 3e-5
    decay_end: float = 0.0
    wsd_decay_steps: int = (
        10000  # NOTE: wsd_decay_steps will only be used when using a wsd-schedule
    )
    warmup_steps: int = 5000
    lr_schedule: str = "wsd"  # supported options: wsd, cos
    vq_reset_thresh: int = 50
    # LAM
    model_dim: int = 512
    ffn_dim: int = 2048
    latent_dim: int = 32
    num_latents: int = 6
    patch_size: int = 16
    num_blocks: int = 4
    num_heads: int = 8
    dropout: float = 0.0
    codebook_dropout: float = 0.0
    param_dtype = jnp.float32
    dtype = jnp.bfloat16
    # Logging
    log: bool = False
    entity: str = ""
    project: str = ""
    name: str = "train_lam"
    tags: list[str] = field(default_factory=lambda: ["lam"])
    log_interval: int = 5
    log_image_interval: int = 250
    ckpt_dir: str = ""
    log_checkpoint_interval: int = 10000
    log_checkpoint_keep_period: int = 20000
    val_data_dir: str = ""
    val_interval: int = 20_000
    val_steps: int = 50
    wandb_id: str = ""
    use_flash_attention: bool = True


args = tyro.cli(Args)


def lam_loss_fn(
    model: LatentActionModel, inputs: dict, training: bool = True
) -> tuple[jax.Array, tuple[jax.Array, jax.Array, dict]]:
    # --- Compute loss ---
    gt = jnp.asarray(inputs["videos"], dtype=jnp.float32) / 255.0
    inputs["videos"] = gt.astype(args.dtype)
    outputs = model(inputs, training=training)
    outputs["recon"] = outputs["recon"].astype(jnp.float32)
    gt_future_frames = gt[:, 1:]
    mse = jnp.square(gt_future_frames - outputs["recon"]).mean()
    q_loss = jnp.square(jax.lax.stop_gradient(outputs["emb"]) - outputs["z"]).mean()
    commitment_loss = jnp.square(
        outputs["emb"] - jax.lax.stop_gradient(outputs["z"])
    ).mean()
    loss = mse + q_loss + args.vq_beta * commitment_loss

    # --- Compute validation metrics ---
    gt = gt_future_frames.clip(0, 1).reshape(-1, *gt_future_frames.shape[2:])
    recon = outputs["recon"].clip(0, 1).reshape(-1, *outputs["recon"].shape[2:])
    psnr = jnp.asarray(pix.psnr(gt, recon)).mean()
    ssim = jnp.asarray(pix.ssim(gt, recon)).mean()
    count_fn = jax.vmap(lambda i: (outputs["indices"] == i).sum())
    index_counts = count_fn(jnp.arange(args.num_latents))
    metrics = dict(
        loss=loss,
        mse=mse,
        q_loss=q_loss,
        commitment_loss=commitment_loss,
        psnr=psnr,
        ssim=ssim,
        codebook_usage=(index_counts != 0).mean(),
    )
    return loss, (outputs["recon"], index_counts, metrics)


@nnx.jit
def train_step(
    lam: LatentActionModel,
    optimizer: nnx.Optimizer,
    inputs: dict,
    action_last_active: jax.Array,
    rng: jax.Array,
) -> tuple[jax.Array, jax.Array, jax.Array, dict]:
    def loss_fn(
        model: LatentActionModel,
    ) -> tuple[jax.Array, tuple[jax.Array, jax.Array, dict]]:
        model.train()
        return lam_loss_fn(model, inputs, training=True)

    # --- Update model ---
    (loss, (recon, idx_counts, metrics)), grads = nnx.value_and_grad(
        loss_fn, has_aux=True
    )(lam)
    optimizer.update(grads)

    # --- Reset inactive latent actions ---
    codebook = lam.vq.codebook
    num_codes = len(codebook)
    active_codes = idx_counts != 0.0
    action_last_active = jnp.where(active_codes, 0, action_last_active + 1)
    p_code = active_codes / active_codes.sum()
    reset_idxs = jax.random.choice(rng, num_codes, shape=(num_codes,), p=p_code)
    do_reset = action_last_active >= args.vq_reset_thresh
    new_codebook = jnp.where(
        jnp.expand_dims(do_reset, -1), codebook[reset_idxs], codebook.value
    )
    lam.vq.codebook.value = new_codebook
    action_last_active = jnp.where(do_reset, 0, action_last_active)
    return loss, recon, action_last_active, metrics

@nnx.jit
def val_step(lam: LatentActionModel, inputs: dict) -> tuple[jax.Array, jax.Array, dict]:
    lam.eval()
    (loss, (recon, _, metrics)) = lam_loss_fn(lam, inputs, training=False)
    return loss, recon, metrics

def calculate_validation_metrics(val_dataloader, lam):
    step = 0
    loss_per_step = []
    metrics_per_step = []
    for videos in val_dataloader:
        inputs = dict(videos=videos)
        loss, recon, metrics = val_step(lam, inputs)
        loss_per_step.append(loss)
        metrics_per_step.append(metrics)
        step += 1
        if step > args.val_steps:
            break

    if step < args.val_steps:
        print(f"Warning: Your validation dataset is too small to make val_steps many steps. Made {step} steps, expected {args.val_steps}")

    val_loss = np.mean(loss_per_step)
    val_metrics = {
        f"val_{key}": np.mean([m[key] for m in metrics_per_step])
        for key in metrics_per_step[0].keys()
    }
    return val_loss, val_metrics, inputs, recon

if __name__ == "__main__":
    jax.distributed.initialize()
    num_devices = jax.device_count()
    if num_devices == 0:
        raise ValueError("No JAX devices found.")
    print(f"Running on {num_devices} devices.")

    if args.batch_size % num_devices != 0:
        raise ValueError(
            f"Global batch size {args.batch_size} must be divisible by "
            f"number of devices {num_devices}."
        )

    per_device_batch_size_for_init = args.batch_size // num_devices

    rng = jax.random.key(args.seed)

    # --- Initialize model ---
    rng, _rng = jax.random.split(rng)
    rngs = nnx.Rngs(_rng)
    lam = LatentActionModel(
        in_dim=args.image_channels,
        model_dim=args.model_dim,
        ffn_dim=args.ffn_dim,
        latent_dim=args.latent_dim,
        num_latents=args.num_latents,
        patch_size=args.patch_size,
        num_blocks=args.num_blocks,
        num_heads=args.num_heads,
        dropout=args.dropout,
        codebook_dropout=args.codebook_dropout,
        param_dtype=args.param_dtype,
        dtype=args.dtype,
        use_flash_attention=args.use_flash_attention,
        rngs=rngs,
    )

    # Count parameters
    _, params, _ = nnx.split(lam, nnx.Param, ...)
    param_counts = count_parameters_by_component(params)

    if args.log and jax.process_index() == 0:
        wandb_init_kwargs = {
            "entity": args.entity,
            "project": args.project,
            "name": args.name,
            "tags": args.tags,
            "group": "debug",
            "config": args,
        }

        if args.wandb_id:
            wandb_init_kwargs.update(
                {
                    "id": args.wandb_id,
                    "resume": "allow",
                }
            )
        wandb.init(**wandb_init_kwargs)

        wandb.config.update({"model_param_count": param_counts})

    print("Parameter counts:")
    print(param_counts)

    # --- Initialize optimizer ---
    lr_schedule = get_lr_schedule(
        args.lr_schedule,
        args.init_lr,
        args.max_lr,
        args.decay_end,
        args.num_steps,
        args.warmup_steps,
        args.wsd_decay_steps,
    )
    tx = optax.adamw(
        learning_rate=lr_schedule,
        b1=0.9,
        b2=0.9,
        weight_decay=1e-4,
        mu_dtype=args.dtype,
    )
    optimizer = nnx.Optimizer(lam, tx)

    # FIXME: switch to create_hybrid_device_mesh for runs spanning multiple nodes
    device_mesh_arr = create_device_mesh((num_devices,))
    mesh = Mesh(devices=device_mesh_arr, axis_names=("data",))

    replicated_sharding = NamedSharding(mesh, PartitionSpec())
    videos_sharding = NamedSharding(mesh, PartitionSpec("data", None, None, None, None))

    model_state = nnx.state(optimizer.model)
    model_sharded_state = jax.lax.with_sharding_constraint(
        model_state, replicated_sharding
    )
    nnx.update(optimizer.model, model_sharded_state)
    optimizer_state = nnx.state(optimizer, nnx.optimizer.OptState)
    optimizer_sharded_state = jax.lax.with_sharding_constraint(
        optimizer_state, replicated_sharding
    )
    nnx.update(optimizer, optimizer_sharded_state)

    # --- Initialize checkpoint manager ---
    step = 0
    handler_registry = ocp.handlers.DefaultCheckpointHandlerRegistry()
    handler_registry.add(
        "model_state", ocp.args.PyTreeSave, ocp.handlers.PyTreeCheckpointHandler
    )
    handler_registry.add(
        "model_state", ocp.args.PyTreeRestore, ocp.handlers.PyTreeCheckpointHandler
    )
    handler_registry.add(
        "train_dataloader_state",
        grain.checkpoint.CheckpointSave,
        cast(ocp.handlers.CheckpointHandler, grain.checkpoint.CheckpointHandler),
    )
    handler_registry.add(
        "train_dataloader_state",
        grain.checkpoint.CheckpointRestore,
        cast(ocp.handlers.CheckpointHandler, grain.checkpoint.CheckpointHandler),
    )
    if args.val_data_dir:
        handler_registry.add(
            "val_dataloader_state",
            grain.checkpoint.CheckpointSave,
            cast(ocp.handlers.CheckpointHandler, grain.checkpoint.CheckpointHandler),
        )
        handler_registry.add(
            "val_dataloader_state",
            grain.checkpoint.CheckpointRestore,
            cast(ocp.handlers.CheckpointHandler, grain.checkpoint.CheckpointHandler),
        )

    checkpoint_options = ocp.CheckpointManagerOptions(
        save_interval_steps=args.log_checkpoint_interval,
        max_to_keep=3,
        keep_period=args.log_checkpoint_keep_period,
        step_format_fixed_length=6,
        cleanup_tmp_directories=True,
    )

    checkpoint_manager = ocp.CheckpointManager(
        args.ckpt_dir,
        options=checkpoint_options,
        handler_registry=handler_registry,
    )

    # --- Create DataLoaderIterator from dataloader ---
    image_shape = (args.image_height, args.image_width, args.image_channels)
    train_iterator = create_dataloader_iterator(args.data_dir, image_shape, args.seq_len, args.batch_size, args.seed)
    if args.val_data_dir:
        val_iterator = create_dataloader_iterator(args.val_data_dir, image_shape, args.seq_len, args.batch_size, args.seed)

    # --- Restore checkpoint ---
    if args.restore_ckpt:
        abstract_optimizer = nnx.eval_shape(lambda: optimizer)
        abstract_optimizer_state = nnx.state(abstract_optimizer)
        if args.val_data_dir:
            restore_args = ocp.args.Composite(
                    model_state=ocp.args.PyTreeRestore(abstract_optimizer_state),  # type: ignore
                    train_dataloader_state=grain.checkpoint.CheckpointRestore(train_iterator),  # type: ignore
                    val_dataloader_state=grain.checkpoint.CheckpointRestore(val_iterator),  # type: ignore
                )
        else: 
            restore_args = ocp.args.Composite(
                    model_state=ocp.args.PyTreeRestore(abstract_optimizer_state),  # type: ignore
                    train_dataloader_state=grain.checkpoint.CheckpointRestore(train_iterator),  # type: ignore
                )
        restored = checkpoint_manager.restore(
            checkpoint_manager.latest_step(),
            args=restore_args
        )
        restored_optimizer_state = restored["model_state"]
        nnx.update(optimizer, restored_optimizer_state)
        train_iterator = restored["train_dataloader_state"]
        if args.val_data_dir:
            val_iterator = restored["val_dataloader_state"]
        step = checkpoint_manager.latest_step() or 0
        print(f"Restored dataloader and model state from step {step}")

    # --- TRAIN LOOP ---
    dataloader_train = (
        jax.make_array_from_process_local_data(videos_sharding, elem)
        for elem in train_iterator
    )

    if args.val_data_dir:
        dataloader_val = (
            jax.make_array_from_process_local_data(videos_sharding, elem)
            for elem in val_iterator
        )
    print(f"Starting training from step {step}...")
    action_last_active = jnp.zeros(args.num_latents, dtype=jnp.int32)
    while step < args.num_steps:
        for videos in dataloader_train:
            # --- Train step ---
            rng, _rng = jax.random.split(rng)

            inputs = dict(videos=videos, rng=_rng)
            rng, _rng = jax.random.split(rng)
            loss, recon, action_last_active, metrics = train_step(
                lam, optimizer, inputs, action_last_active, _rng
            )
            metrics["lr"] = lr_schedule(step)
            print(f"Step {step}, loss: {loss}")
            step += 1

            # --- Validation loss ---
            if args.val_data_dir and step % args.val_interval == 0:
                print(f"Calculating validation metrics...")
                val_loss, val_metrics, val_gt_batch, val_recon = calculate_validation_metrics(dataloader_val, lam)
                print(f"Step {step}, validation loss: {val_loss}")

            # --- Logging ---
            if args.log:
                if step % args.log_interval == 0 and jax.process_index() == 0:
                    log_dict = {
                        "loss": loss,
                        "step": step,
                        **metrics
                        }
                    if args.val_data_dir and step % args.val_interval == 0:
                        log_dict.update({
                            "val_loss": val_loss,
                            **val_metrics
                        })
                    wandb.log(log_dict)
                if step % args.log_image_interval == 0:
                    gt_seq = inputs["videos"][0, 1:].astype(jnp.float32) / 255.0
                    recon_seq = recon[0].clip(0, 1)
                    comparison_seq = jnp.concatenate((gt_seq, recon_seq), axis=1)
                    comparison_seq = einops.rearrange(
                        comparison_seq * 255, "t h w c -> h (t w) c"
                    )
                    if args.val_data_dir and step % args.val_interval == 0:
                        gt_seq_val = val_gt_batch["videos"][0, 1:].astype(jnp.float32) / 255.0
                        recon_seq_val = val_recon[0].clip(0, 1)
                        val_comparison_seq = jnp.concatenate((gt_seq, recon_seq), axis=1)
                        val_comparison_seq = einops.rearrange(
                            val_comparison_seq * 255, "t h w c -> h (t w) c"
                        )
                    # NOTE: Process-dependent control flow deliberately happens
                    # after indexing operation since it must not contain code
                    # sections that lead to cross-accelerator communication.
                    if jax.process_index() == 0:
                        log_images = dict(
                            image=wandb.Image(np.asarray(gt_seq[0])),
                            recon=wandb.Image(np.asarray(recon_seq[0])),
                            true_vs_recon=wandb.Image(
                                np.asarray(comparison_seq.astype(np.uint8))
                            ),
                        )
                        if args.val_data_dir and step % args.val_interval == 0:
                            log_images.update(
                                dict(
                                    val_image=wandb.Image(np.asarray(gt_seq_val[0])),
                                    val_recon=wandb.Image(np.asarray(recon_seq_val[0])),
                                    val_true_vs_recon=wandb.Image(
                                        np.asarray(val_comparison_seq.astype(np.uint8))
                                    )
                                )
                            )
                        wandb.log(log_images)
            # --- Checkpointing ---
            if args.save_ckpt and step % args.log_checkpoint_interval == 0:
                optimizer_state = nnx.state(optimizer)
                if args.val_data_dir:
                    ckpt_manager_args = ocp.args.Composite(
                        model_state=ocp.args.PyTreeSave(optimizer_state),  # type: ignore
                        train_dataloader_state=grain.checkpoint.CheckpointSave(  # type: ignore
                            train_iterator  # type: ignore
                        ),
                        val_dataloader_state=grain.checkpoint.CheckpointSave(  # type: ignore
                            val_iterator  # type: ignore
                        )
                    )
                else: 
                    ckpt_manager_args = ocp.args.Composite(
                        model_state=ocp.args.PyTreeSave(optimizer_state),  # type: ignore
                        train_dataloader_state=grain.checkpoint.CheckpointSave(  # type: ignore
                            train_iterator  # type: ignore
                        )
                    )
                checkpoint_manager.save(
                    step,
                    args=ckpt_manager_args
                    )
                print(f"Saved checkpoint at step {step}")
            if step >= args.num_steps:
                break

    checkpoint_manager.close()