LaMPlace: Learning to Optimize Cross-Stage Metrics in Macro Placement

Authors: Zijie Geng, Jie Wang, Ziyan Liu, Siyuan Xu, Zhentao Tang, Shixiong Kai, Mingxuan Yuan, Jianye HAO, Feng Wu
Primary area: applications to robotics, autonomy, planning
Keywords: Macro placement, Chip design, EDA

Abstract:
Machine learning techniques have shown great potential in enhancing macro placement, a critical stage in modern chip design.
However, existing methods primarily focus on *online* optimization of *intermediate surrogate metrics* that are available at the current placement stage, rather than directly targeting the *cross-stage metrics*---such as the timing performance---that measure the final chip quality.
This is mainly because of the high computational costs associated with performing post-placement stages for evaluating such metrics, making the *online* optimization impractical.
Consequently, these optimizations struggle to align with actual performance improvements and can even lead to severe manufacturing issues.
To bridge this gap, we propose **LaMPlace**, which **L**earns **a** **M**ask for optimizing cross-stage metrics in macro placement.
Specifically, LaMPlace trains a predictor on *offline* data to estimate these *cross-stage metrics* and then leverages the predictor to quickly generate a mask, i.e., a pixel-level feature map that quantifies the impact of placing a macro in each chip grid location on the design metrics.
This mask essentially acts as a fast evaluator, enabling placement decisions based on *cross-stage metrics* rather than *intermediate surrogate metrics*.
Experiments on commonly used benchmarks demonstrate that LaMPlace significantly improves the chip quality across several key design metrics, achieving an average improvement of 9.6\%, notably 43.0\% and 30.4\% in terms of WNS and TNS, respectively, which are two crucial cross-stage metrics that reflect the final chip quality in terms of the timing performance.

Decision: accept (oral)
Reviewer scores: 6, 8, 8, 8

Reviews and discussion:
<thread>
creation date:
1730264631373

thread_type:
official_review

<thread_object>
creator: reviewer_xpkq

<content>
summary:
The paper introduces LaMPlace, a novel method for macro placement in chip design that focuses on optimizing cross-stage metrics, such as timing performance, which are crucial for the final chip quality. LaMPlace addresses this by learning a mask that guides the placement process based on cross-stage metrics. The proposed method involves (1) training a predictor on offline data to estimate cross-stage metrics, and (2) using this predictor to generate a mask, which is a pixel-level feature map that quantifies the impact of placing a macro in each chip grid location on the design metrics. This mask enables placement decisions based on cross-stage metrics rather than intermediate surrogate metrics. The paper demonstrates the effectiveness of LaMPlace on commonly used benchmarks, showing improvements in chip quality across several key design metrics, including WNS and TNS.

strengths:
1. The paper introduces a unique approach to macro placement that directly addresses the optimization of cross-stage metrics, crucial for the final chip quality. Existing methods often focus on optimizing intermediate surrogate metrics, which can lead to sub-optimal chip quality.
2. The proposed method, LaMPlace, has been demonstrated to be effective in improving chip quality across several key design metrics, including WNS and TNS, which are crucial for timing performance. The paper provides great empirical results on commonly used benchmarks, showing significant improvements in chip quality.
3. The use of a mask for placement optimization allows for efficient placement decisions based on cross-stage metrics. It enables the optimization of cross-stage metrics without incurring the high computational costs associated with existing methods.
4. The paper acknowledges the practicality of its approach for industry applications. It emphasizes that the offline setting for training the predictor is feasible due to the availability of substantial chip data from design projects.

weaknesses:
1. Reliance on Offline Data. The paper's approach relies on the availability of substantial offline chip data for training the predictor. While the paper argues that this is practical in the industry, it may limit the applicability of the method in scenarios where such data is scarce or unavailable. Addressing this limitation, either through data augmentation techniques or alternative training strategies, would enhance the paper's broader impact.

2. Black-Box Nature of the Predictor. The predictor used in LaMPlace is a black box, meaning its internal workings and decision-making processes are not transparent. This lack of interpretability may make it difficult to understand why certain placement decisions are made, potentially hindering further improvements or debugging of the method. Specifically, did authors find strange examples, which are difficult for human experts to understand?

3. Limited Discussion of Scalability. The paper does not explicitly discuss the scalability of LaMPlace to very large-scale designs with millions of cells. While the method shows promising results on the tested benchmarks, further analysis of its computational complexity and memory requirements for larger designs would be beneficial.

questions:
1. Ablation study on the size of the offline dataset. What are the results with different sizes of offline dataset?
2. The authors claim that they will release the code once the paper is accepted. Is it possible to discuss more implementation details or release the code for review?
</content>
</thread_object>

</thread>
<thread>
creation date:
1730550002098

thread_type:
official_review

<thread_object>
creator: reviewer_pziw

<content>
summary:
This work proposes a novel learning-based macro placement algorithm which learn a mask to optimize multiple cross-stage metrics. The performance of this algorithm is significant especially as the timing metrics, i.e., TNS and WNS.

strengths:
1. The idea of L-flow and L-mask is novel and the improvement is significant.
2. Comprehensive experiment and analysis.

weaknesses:
Some parts of technical contents and experimental settings should be explained.

questions:
Thanks to the authors’ contributions for proposing this novel macro placement algorithm and performing comprehensive experiments. Meanwhile, this paper is well-written and easy to read.

I still have some questions about the technical contents and experimental settings.

1. “Notably, this function is translation-invariant with respect to the macro positions.“ Even if the relative positions of two macros remain unchanged for chip placement, the final design metrics (e.g., congestion and timing) will still change. This is because the macros' positions relative to the chip boundary affect the placement of other standard cells. Therefore, I wonder if there is a more detailed explanation of “translation-invariant”.
2. More explanation about pair-wise ranking could be included in the paper.
3. The final metric "HPWL" often serves as a surrogate metric in the design flow. "Wirelength" is a common final metric, that most people are concerned with, to replace "HPWL".
</content>
</thread_object>

</thread>
<thread>
creation date:
1730698111286

thread_type:
official_review

<thread_object>
creator: reviewer_cjoe

<content>
summary:
This paper introduces LaMPlace, a machine learning-based approach to optimize macro placement in EDA by focusing on cross-stage metrics that impact the final quality of chip designs. Traditional methods often optimize surrogate metrics, which are simpler to compute but do not directly correlate with final chip performance. LaMPlace tackles this by training a predictor to estimate these cross-stage metrics offline and generating a pixel-level mask to inform placement decisions efficiently. This work improved timing performance metrics like WNS and TNS, etc. Experimental results demonstrate that LaMPlace achieves significant improvements, with an average increase of 9.6% across key metrics.

strengths:
Focus on final metrics and thus improved results: LaMPlace addresses a critical gap by targeting final chip quality metrics rather than intermediate surrogate metrics.

Efficiency: By using a pre-trained predictor, the proposed method reduces the high computational cost associated with evaluating cross-stage metrics during placement.

Zero-shot Generalization: The method demonstrates strong generalization on unseen benchmarks, showing adaptability without extensive fine-tuning.

weaknesses:
Computational Complexity: Despite its efficiency improvements, the approach still relies on a complex training phase that may limit its practical applications in resource-constrained environments.

Potential Overhead in Prediction: Generating the placement mask may still introduce additional computational overhead, particularly when applied to larger, more complex designs.

questions:
None
</content>
</thread_object>

</thread>
<thread>
creation date:
1730711829216

thread_type:
official_review

<thread_object>
creator: reviewer_wag4

<content>
summary:
This paper presents LaMPlace, a novel machine learning method aimed at enhancing macro placement in chip design by prioritizing cross-stage metrics, such as timing performance, over intermediate metrics. The approach employs an offline-trained predictor to generate a pixel-level mask that evaluates the impact of macro placements on design metrics, followed by a greedy algorithm for placement optimization. Experimental results demonstrate a noteworthy average improvement of 9.6% in chip quality, with significant enhancements of 43.0% in WNS and 30.4% in TNS.

strengths:
+ The method shows strong zero-shot inference capabilities, allowing for effective generalization to unseen designs without requiring extensive training samples in the offline phase.
+ It successfully optimizes cross-stage metrics, including HPWL, WNS, and TNS, concurrently, which is a significant advancement in macro placement techniques.

weaknesses:
- The algorithm struggles with placing macros that are not edge-connected, limiting its effectiveness in scenarios where macros do not have interconnections.

questions:
- In Figure 9, related to DREAMPlace, there are blank rectangular areas, and some macros appear to overlap. Could you clarify this observation? Additionally, could you provide visualized results for the baseline method?
- The timing-driven option in DREAMPlace does not seem to support macros effectively. Can you present results with this option disabled?
- How does LaMPlace handle macros that are smaller than the grid size?
- Some tables, such as Table 4 and Table 8, are missing units. Could you rectify this oversight?
</content>
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</thread>


Metareview:
metareview:
The paper introduces LaMPlace, a novel machine learning framework for macro placement in chip design, which optimizes cross-stage metrics like timing performance. By training an offline predictor to estimate cross-stage metrics and generating a pixel-level placement mask, LaMPlace outperforms traditional methods in improving final chip quality metrics. All reviewers recommend acceptance (6,8,8,8). Strengths listed include the paper's novelty, comprehensive experiments, and strong alignment with industry practices. Criticisms include the reliance on offline training data, the predictor's black-box nature, and limited scalability discussions. The authors effectively addressed these criticisms during the rebuttal, highlighting the feasibility of offline training in industrial contexts, explaining the interpretability of the predictor outputs, and elaborating on scalability considerations. I follow the reviewers strong endorsement and recommend acceptance as an oral.