REVIEW 3 major objections 5 minor 4 cited by
Hardware Scaling Trends and Diminishing Returns in Large-Scale Distributed Training
T0 review · 3 major / 5 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read Beyond roughly 128 GPUs, model parallelism outperforms data-parallel sharding for LLM training.
desk verdict Solid, wide-ranging FSDP scaling study with a real finding; the headline claim of 'properly optimized' overreaches past the untested HSDP family. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the exposed-communication mechanism of Fully Sharded Data Parallelism: parameter materialization and gradient reduction go through NCCL AllGather and ReduceScatter collectives, which use ring algorithms whose latency scales with node count (measured in Figure 2), unlike the tree-based AllReduce used by standard data parallelism and tensor parallelism. Because communication-bound kernels cannot be hidden by computation once the per-device compute time is small relative to collective latency, exposed communication grows and hardware utilization collapses. Model parallelism is the lever that shrinks the FSDP collective's world size, trading AllReduce and pipeline-bubble costs for reduced AllGather/ReduceScatter volume, which the paper measures as lower exposed communication and higher global throughput.
What would settle it
Train Llama-7B at 2048 H100 GPUs with hybrid sharded data parallelism (sharding only within a node) or with ZeRO-3 using node-local sharding, under the same fixed global batch size and measured with the paper's methodology, and compare per-GPU throughput and MFU to the paper's best tensor-parallel configuration. If per-GPU throughput fails to decline by roughly a third relative to 128 GPUs, or MFU stays above 40%, the claimed diminishing returns under proper optimization would not hold.
Extended reading notes
Core claim
The central discovery is that communication boundedness, not compute, governs large-scale FSDP training. The AllGather and ReduceScatter collectives used to rematerialize and update sharded parameters are ring-based and their latency grows with world size, so as nodes are added the ratio of communication to computation rises; beyond 128 H100 GPUs for a 7B model, exposed communication is unavoidable, hardware utilization (MFU) falls, and throughput per device drops by 37.22% when scaling from 128 to 2048 GPUs. Because GPU power draw declines only slightly (5.87%) while throughput falls, tokens per watt decline markedly. The paper shows that moderate model parallelism (tensor or pipeline degrees 2–4) shrinks the data-parallel group sizes for FSDP collectives and thereby reduces exposed communication, improving throughput, MFU, and power efficiency relative to the data-parallel baseline—including a +52.60% words-per-second gain at 2048 GPUs. It also shows that faster compute relative to interconnect (H100 vs A100) worsens communication boundedness, and that scaling model size increases both compute and communication jointly.
Load-bearing premise
The claim that returns diminish 'even when hardware and parallelization strategies are properly optimized' assumes the tested sweep over tensor and pipeline parallelism (degrees up to 16 on fixed node counts) covers the strategies a truly optimized system would use; the paper does not test hybrid sharded data parallelism, ZeRO-3 with different sharding policies, or newer fabric topologies, any of which could in principle flatten the diminishing-returns curve.
Editorial extensions
If this is right
- Practitioners training 7B-class models on clusters above roughly 128 GPUs should add tensor parallelism at degree 2 or 4 instead of relying on FSDP data-parallel replicas, because it reduces exposed communication and raises global throughput.
- Throughput-based scaling laws that assume linear gains with added accelerators will overestimate output at pretraining scale; compute-optimal scaling should incorporate communication cost.
- Energy per token rises with cluster size, so the environmental cost of a training run is not proportional to FLOPs but to a less favorable curve.
- Faster GPU compute alone will not fix the problem; interconnect and memory bandwidth improvements are needed to prevent training from becoming more communication-bound.
Reading between the lines
- The untested strategies the paper defers, especially hybrid sharded data parallelism that keeps AllGather inside a node, could plausibly shift the crossover point where model parallelism becomes preferable; the reported curves may be an upper bound on what current FSDP-like training can achieve.
- The diminishing-returns pattern likely extends to TPU-based training and to inference-time parallel decoding, because the same ring-collective latency growth applies whenever sharded parameters must be gathered across many devices.
- A testable design implication is that node-local sharding with inter-node only AllReduce—the hybrid pattern—should recover much of the lost throughput, which would directly quantify how much of the reported 37% drop is due to the ring AllGather world size.
- Scaling-law papers that ignore communication will increasingly mispredict time-to-train as clusters grow; replacing FLOP count with a communication-aware cost measure is a tractable near-term correction.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper presents an extensive empirical study of distributed training of Llama-2-style LLMs (1B to 70B parameters) on clusters ranging from 8 to 2048 H100/A100 GPUs, using PyTorch FSDP combined with optional tensor and pipeline parallelism. The central measurements are global and per-device throughput, exposed communication (from profiled NCCL/CUDA kernel times), MFU, and GPU power draw. The paper reports three main findings: (1) FSDP's AllGather/ReduceScatter communication overhead grows with data-parallel world size, making model parallelism (tensor or pipeline, at degrees 2--4) beneficial at scales beyond roughly 128 GPUs; (2) global throughput increases sublinearly with added accelerators while per-GPU power draw remains nearly flat, so tokens-per-watt and MFU decline with scale; and (3) the optimal configurations for sharded training differ from earlier recommendations that model parallelism be avoided. The abstract and conclusion generalize these results to claim that scaling accelerators yields diminishing returns 'even when hardware and parallelization strategies are properly optimized.'
Significance. If the conclusions hold, they provide actionable guidance for training large models at scale: flat FSDP becomes communication-bound above a few hundred GPUs, and moderate tensor/pipeline parallelism is preferable; they also highlight an energy-efficiency penalty of scale that is largely absent from existing scaling-law discussions. The paper's strengths are the unusual scale of the measurements (up to 2048 H100s), the breadth across model sizes and hardware generations, the detailed kernel-level accounting of exposed communication, and the fact that the trends are direct observations rather than outputs of a fitted parametric model. The central caveat is that the 'properly optimized' claim is conditional on a limited strategy family; this affects the generality of the diminishing-returns conclusion, not the validity of the measurements themselves.
major comments (3)
- [Abstract, §4.3, Appendix A] The abstract and Section 5 assert diminishing returns 'even when hardware and parallelization strategies are properly optimized,' but the optimization search in Section 4.3 is restricted to tensor and pipeline parallelism of degree at most 16 combined with a flat FSDP sharding group. Appendix A explicitly defers Hybrid Sharded Data Parallelism (HSDP) and other hierarchical sharding strategies to future work. This is not a peripheral omission: Sections 2.2 and Figure 2 identify AllGather/ReduceScatter world size as the scaling bottleneck, and HSDP is precisely a way to keep those collectives inside 8-GPU nodes. If HSDP (or a similar hierarchical scheme) performs sufficiently better at 2048 GPUs, the reported diminishing-returns curve and the +52.60% improvement from tensor parallelism may not represent the 'properly optimized' configuration. The measurements remain valid as a characterization of flat FSDP, but the general claim should be scoped to the considered parallelism family, or HSDP experiments should be added at the largest scales.
- [§3 (Metrics), §4.1, §4.3] Section 3 states that metrics are aggregated over 50 training iterations after 10 warmup iterations, but this appears to be a single run and no run-to-run variance or confidence intervals are reported. Because the central quantitative claims (e.g., the 37.22% per-device throughput decrease from 128 to 2048 GPUs in Section 4.1 and the +52.60% WPS improvement from tensor parallelism in Section 5) are used to support the diminishing-returns conclusion, the absence of variance information makes it impossible to judge whether the differences between configurations are statistically significant. Please report standard deviations over at least a few repeated runs (or justify why the environment is deterministic and demonstrate this with measurements).
- [§4.2, Figure 5] Section 4.2 and Figure 5 describe strong scaling with a 'fixed global batch size of 32 examples' across 2 to 32 nodes, but with 256 GPUs and global batch 32, a pure data-parallel configuration would require a sub-unit per-device batch. Presumably the optimal configurations use enough model parallelism to keep the data-parallel degree no larger than 32, but the text does not state how the configurations were re-searched per node count. The caption also says the optimal strategy is 'determined by the experimental results displayed in Figure 6,' which is for a different setup (256 GPUs, global batch 512). Please clarify the selection procedure and the feasibility of the global batch at each scale; this is load-bearing for the strong-scaling results.
minor comments (5)
- [Introduction, Related Work] There are several typos and inconsistencies: 'langauge' in the introduction, 'Zero-3' instead of 'ZeRO-3' in Section 6, and inconsistent capitalization of 'FLOPS'/'FLOPs' throughout.
- [§2.2, Figure 2, Appendix B] The units for AllReduce/AllGather bandwidth in Figure 2 are reported as GB/s, while Appendix B refers to per-node InfiniBand bandwidth in GB/s; please clarify whether these are GB/s or Gb/s, and whether the 'favorable scaling' of AllReduce bandwidth is specific to the tree algorithm or a general statement.
- [§4.4] The text says 'nearly 20% decrease in hardware utilization' when comparing A100 to H100 (59.67% to 40.77%). This is a decrease of about 19 percentage points but roughly 32% relative; please report the relative and absolute changes explicitly to avoid ambiguity.
- [§3 (Power utilization)] Power efficiency is based on NVML GPU power draw only; the paper should state explicitly that total system power (including CPU, memory, and network) is not included, so the energy-efficiency claims apply to GPU power consumption.
- [Appendix F, Figure 13] In Figure 13, the y-axis for 'Exposed Communication' is labeled 'Time (microseconds)' but the values are on the order of 1e6, which is inconsistent; the unit is likely milliseconds. Please fix the axis label.
Circularity Check
No circularity: the scaling and parallelization conclusions are direct measurements, not fitted predictions or self-citation reductions.
full rationale
The paper's central claims are empirical rather than derivational: throughput, MFU, power draw, and NCCL kernel times are measured across hardware scales, model sizes, and parallelization strategies and reported directly (Figures 3, 5, 6, 8). The conclusion that FSDP becomes communication-bound at scale follows from measured AllGather/ReduceScatter scaling and measured exposed communication, not from a parameter fitted to the target claim. Selecting the best observed tensor/pipeline configuration at each scale in Sections 4.2-4.3 is ordinary empirical search; the diminishing-returns curve is the measured envelope of searched strategies, not a quantity defined in terms of itself. The only self-references (Fernandez et al. 2023; Strubell et al. 2019) appear in related-work and environmental-impact context and are not load-bearing for the scaling results. Appendix A explicitly defers Hybrid Sharded Data Parallelism and variable fabric speeds to future work, which is a genuine external-validity caveat on the phrase 'even when hardware and parallelization strategies are properly optimized'; the conclusion is conditioned on the tested strategy family. That incompleteness is a correctness risk, not circularity, because no step in the paper reduces by construction to its own input.
Assumptions & free parameters
assumptions (5)
- domain assumption The measured clusters and software stack are representative of typical datacenter training platforms.
- ad hoc to paper Fifty measured training iterations after ten warmup iterations yield steady-state performance metrics.
- domain assumption The profiler-based separation of exposed versus overlapped communication correctly captures hardware stalls.
- domain assumption Llama-2 is a representative decoder-only architecture for scaling conclusions.
- ad hoc to paper The parallelization search space considered, tensor and pipeline parallelism up to degree 16, contains the optimal configurations for the studied workloads.
Cite this review
Pith. "Pith review of Hardware Scaling Trends and Diminishing Returns in Large-Scale Distributed Training." pith.science (2026). https://pith.science/paper/V4ACOPCX
@misc{pith2026241113055,
author = {Pith},
title = {Pith review of: Hardware Scaling Trends and Diminishing Returns in Large-Scale Distributed Training},
year = {2026},
howpublished = {\url{https://pith.science/paper/V4ACOPCX}},
note = {Machine review of arXiv:2411.13055}
}
read the original abstract
Dramatic increases in the capabilities of neural network models in recent years are driven by scaling model size, training data, and corresponding computational resources. To develop the exceedingly large networks required in modern applications, such as large language models (LLMs), model training is distributed across tens of thousands of hardware accelerators (e.g. GPUs), requiring orchestration of computation and communication across large computing clusters. In this work, we demonstrate that careful consideration of hardware configuration and parallelization strategy is critical for effective (i.e. compute- and cost-efficient) scaling of model size, training data, and total computation. We conduct an extensive empirical study of the performance of large-scale LLM training workloads across model size, hardware configurations, and distributed parallelization strategies. We demonstrate that: (1) beyond certain scales, overhead incurred from certain distributed communication strategies leads parallelization strategies previously thought to be sub-optimal in fact become preferable; and (2) scaling the total number of accelerators for large model training quickly yields diminishing returns even when hardware and parallelization strategies are properly optimized, implying poor marginal performance per additional unit of power or GPU-hour.
Forward citations
Cited by 4 Pith papers
-
Compute-Optimal Is Not Cluster-Optimal: Systems-Aware Scaling for Sparse Mixture-of-Experts
Under a fixed model-FLOPs budget, the fitted loss for sparse MoE models decreases monotonically with sparsity, so the optimum sits at the boundary; an interior sparsity optimum appears only when hardware-deliverable F...
-
Evaluating MFU as a Proxy for GPU Power for Energy-Aware Simulation of LLM Training
MFU is a valid linear predictor of GPU power in compute-bound LLM training, with per-(GPU, dtype, batch) fits reaching 1% error, matching measurement noise.
-
Quantifying the Energy Consumption and Carbon Emissions of LLM Inference via Simulations
A simulation framework couples an LLM inference simulator with a GPU power model and an energy-grid co-simulator to estimate energy and carbon emissions across deployment configurations.
-
Estudio de la eficiencia en la escalabilidad de GPUs para el entrenamiento de Inteligencia Artificial
Using MLPerf v4.1 data, the paper shows that per-GPU efficiency declines as GPU count grows, and it identifies intermediate configurations that balance training speed and resource use.
Reference graph
Works this paper leans on
-
[5]
The framework tax: Disparities between inference efficiency in nlp research and deployment
Jared Fernandez, Jacob Kahn, Clara Na, Yonatan Bisk, and Emma Strubell. The framework tax: Disparities between inference efficiency in nlp research and deployment. InThe 2023 Conference on Empirical Methods in Natural Language Processing,
work page 2023
-
[6]
Association for Computing Machinery. ISBN 9781450357999. doi: 10.1145/3210377.3210394. URL https://doi.org/10.1145/3210377.3210394. IBM Granite Team. Granite 3.0 language models,
-
[9]
John L Hennessy and David A Patterson.Computer architecture: a quantitative approach
URLhttps://arxiv.org/abs/1806.03377. John L Hennessy and David A Patterson.Computer architecture: a quantitative approach. Morgan kaufmann,
-
[12]
Sasha Luccioni, Yacine Jernite, and Emma Strubell
URLhttps://arxiv.org/abs/2302.08476. Sasha Luccioni, Yacine Jernite, and Emma Strubell. Power hungry processing: Watts driving the cost of ai deployment? In The 2024 ACM Conference on Fairness, Accountability, and Transparency, pp. 85–99,
arXiv 2024
-
[13]
Myle Ott, Sam Shleifer, Min Xu, Priya Goyal, Quentin Duval, and Vittorio Caggiano. Fully sharded data parallel: faster ai training with fewer gpus — engineering.fb.com.https://engineering.fb.com/2021/07/15/open-source/fsdp/,
work page 2021
-
[15]
Tomer Porian, Mitchell Wortsman, Jenia Jitsev, Ludwig Schmidt, and Yair Carmon. Resolving discrepancies in compute-optimal scaling of language models.arXiv preprint arXiv:2406.19146,
-
[16]
Noam Shazeer, Azalia Mirhoseini, Krzysztof Maziarz, Andy Davis, Quoc Le, Geoffrey Hinton, and Jeff Dean. Outrageously large neural networks: The sparsely-gated mixture-of-experts layer.arXiv preprint arXiv:1701.06538,
-
[17]
Mohammad Shoeybi, Mostofa Patwary, Raul Puri, Patrick LeGresley, Jared Casper, and Bryan Catanzaro
URLhttps://arxiv.org/abs/1811.02084. Mohammad Shoeybi, Mostofa Patwary, Raul Puri, Patrick LeGresley, Jared Casper, and Bryan Catanzaro. Megatron- lm: Training multi-billion parameter language models using model parallelism.ArXiv, abs/1909.08053,
arXiv 1909
Show all 25 references
-
[18]
Sebastian U Stich
URL https://api.semanticscholar.org/CorpusID:202660670. Sebastian U Stich. Local sgd converges fast and communicates little.arXiv preprint arXiv:1805.09767,
-
[19]
doi: 10.18653/v1/P19-1355
Association for Computational Linguistics. doi: 10.18653/v1/P19-1355. URL https://aclanthology.org/P19-1355. Yi Tay, Mostafa Dehghani, Samira Abnar, Hyung Won Chung, William Fedus, Jinfeng Rao, Sharan Narang, Vinh Q. Tran, Dani Yogatama, and Donald Metzler. Scaling laws vs mod...
-
[20]
Accessed: 2023-05-05
URL www.mosaicml.com/blog/mpt-7b. Accessed: 2023-05-05. Vijay Thakkar, Pradeep Ramani, Cris Cecka, Aniket Shivam, Honghao Lu, Ethan Yan, Jack Kosaian, Mark Hoemmen, Haicheng Wu, Andrew Kerr, Matt Nicely, Duane Merrill, Dustyn Blasig, Fengqi Qiao, Piotr Majcher, Paul Springer, ...
2023
-
[21]
Hugo Touvron, Louis Martin, Kevin Stone, Peter Albert, Amjad Almahairi, Yasmine Babaei, Nikolay Bashlykov, Soumya Batra, Prajjwal Bhargava, Shruti Bhosale, et al
URLhttps://github.com/NVIDIA/ cutlass. Hugo Touvron, Louis Martin, Kevin Stone, Peter Albert, Amjad Almahairi, Yasmine Babaei, Nikolay Bashlykov, Soumya Batra, Prajjwal Bhargava, Shruti Bhosale, et al. Llama 2: Open foundation and fine-tuned chat models. arXiv preprint arXiv:2...
-
[22]
Context parallelism for scalable million-token inference.arXiv preprint arXiv:2411.01783,
Amy Yang, Jingyi Yang, Aya Ibrahim, Xinfeng Xie, Bangsheng Tang, Grigory Sizov, Jeremy Reizenstein, Jongsoo Park, and Jianyu Huang. Context parallelism for scalable million-token inference.arXiv preprint arXiv:2411.01783,
-
[23]
Accelerating the training of large language models using efficient activation rematerialization and optimal hybrid parallelism
14 Tailing Yuan, Yuliang Liu, Xucheng Ye, Shenglong Zhang, Jianchao Tan, Bin Chen, Chengru Song, and Di Zhang. Accelerating the training of large language models using efficient activation rematerialization and optimal hybrid parallelism. In 2024 USENIX Annual Technical Confer...
2024
-
[24]
For our primary experiments, we trained models using PyTorch 2.3.1 built with CUDA 12.1, with attention implementation provided by XFormers 0.27
and xFormers (Lefaudeux et al., 2022). For our primary experiments, we trained models using PyTorch 2.3.1 built with CUDA 12.1, with attention implementation provided by XFormers 0.27. We utilize PyTorch FSDPv2 with prefetch of subsequent layers enabled. For the A100 and H100 ...
2022
-
[25]
Nodes within the V100 cluster consist of 8-GPU setups connected with first-generation NVLink in a Hybrid Cube Mesh (HCM) topology
attention kernels on Volta hardware – due to limited hardware support on older Volta hardware. Nodes within the V100 cluster consist of 8-GPU setups connected with first-generation NVLink in a Hybrid Cube Mesh (HCM) topology. We compute the runtime of communication and computa...
2024
-
[1988]
Efficient parallelization layouts for large-scale distributed model training.arXiv preprint arXiv:2311.05610,
Johannes Hagemann, Samuel Weinbach, Konstantin Dobler, Maximilian Schall, and Gerard de Melo. Efficient parallelization layouts for large-scale distributed model training.arXiv preprint arXiv:2311.05610,
-
[2000]
Olmo: Accelerating the science of language models.arXiv preprint arXiv:2402.00838,
11 Dirk Groeneveld, Iz Beltagy, Pete Walsh, Akshita Bhagia, Rodney Kinney, Oyvind Tafjord, Ananya Harsh Jha, Hamish Ivison, Ian Magnusson, Yizhong Wang, et al. Olmo: Accelerating the science of language models.arXiv preprint arXiv:2402.00838,
-
[2018]
Zhenkun Cai, Xiao Yan, Kaihao Ma, Yidi Wu, Yuzhen Huang, James Cheng, Teng Su, and Fan Yu
URLhttp://github.com/jax-ml/jax. Zhenkun Cai, Xiao Yan, Kaihao Ma, Yidi Wu, Yuzhen Huang, James Cheng, Teng Su, and Fan Yu. Tensoropt: Exploring the tradeoffs in distributed dnn training with auto-parallelism.IEEE Transactions on Parallel and Distributed Systems, 33(8):1967–1981,
1967
-
[2019]
Scaling laws for neural language models.arXiv preprint arXiv:2001.08361,
Jared Kaplan, Sam McCandlish, Tom Henighan, Tom B Brown, Benjamin Chess, Rewon Child, Scott Gray, Alec Radford, Jeffrey Wu, and Dario Amodei. Scaling laws for neural language models.arXiv preprint arXiv:2001.08361,
2001 arXiv
-
[2020]
Branch-train-merge: Embarrassingly parallel training of expert language models
Margaret Li, Suchin Gururangan, Tim Dettmers, Mike Lewis, Tim Althoff, Noah A Smith, and Luke Zettlemoyer. Branch-train-merge: Embarrassingly parallel training of expert language models. InFirst Workshop on Interpolation Regularizers and Beyond at NeurIPS 2022,
2022
-
[2021]
Training deep nets with sublinear memory cost.arXiv preprint arXiv:1604.06174,
Tianqi Chen, Bing Xu, Chiyuan Zhang, and Carlos Guestrin. Training deep nets with sublinear memory cost.arXiv preprint arXiv:1604.06174,
-
[2022]
Diloco: Distributed low-communication training of language models
Arthur Douillard, Qixuan Feng, Andrei A Rusu, Rachita Chhaparia, Yani Donchev, Adhiguna Kuncoro, Marc’Aurelio Ranzato, Arthur Szlam, and Jiajun Shen. Diloco: Distributed low-communication training of language models. arXiv preprint arXiv:2311.08105,
-
[2023]
The llama 3 herd of models.arXiv preprint arXiv:2407.21783,
Abhimanyu Dubey, Abhinav Jauhri, Abhinav Pandey, Abhishek Kadian, Ahmad Al-Dahle, Aiesha Letman, Akhil Mathur, Alan Schelten, Amy Yang, Angela Fan, et al. The llama 3 herd of models.arXiv preprint arXiv:2407.21783,
-
[2024]
Saptadeep Pal, Eiman Ebrahimi, Arslan Zulfiqar, Yaosheng Fu, Victor Zhang, Szymon Migacz, David Nellans, and Puneet Gupta
[Accessed 30-09-2024]. Saptadeep Pal, Eiman Ebrahimi, Arslan Zulfiqar, Yaosheng Fu, Victor Zhang, Szymon Migacz, David Nellans, and Puneet Gupta. Optimizing multi-gpu parallelization strategies for deep learning training.Ieee Micro, 39(5):91–101,
2024
Reviewed August 12, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.