REVIEW 3 major objections 5 minor 40 references
Towards Sustainable Large Language Model Serving
T0 review · 3 major / 5 minor · reviewed 2026-08-10 · deepseek-v4-flash
Pith's one-line read This paper claims that for compute-light LLM serving workloads, an older, slower GPU can consume less energy than a newer flagship GPU, and that once manufacturing emissions are included, older hardware can yield lower total carbon in…
desk verdict A genuinely useful GPU-energy measurement study whose 'total carbon' headline overreaches the GPU-only power data; worth a serious referee if the accounting boundary is fixed. 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 mechanism is a two-term carbon model rather than a single energy number. Operational carbon is energy times grid carbon intensity ($C_{\mathrm{op}} = E\cdot CI$); embodied carbon is the manufacturing carbon of the GPU, estimated from chip area and memory via an architectural carbon model, discounted by the fraction of the GPU's lifetime a prompt occupies ($C_{\mathrm{em}} = (t/LT)\cdot C_{\mathrm{em,GPU}}$). Because T4 draws up to only 70 W against RTX6000 Ada's 300 W TDP, a light batch-size-1 load runs almost as fast on T4 while using less power, and its smaller chip area and memory give it roughly 2.6x lower embodied carbon (10.3 kg vs 26.6 kg). The argument is carried by this power-versus-time tradeoff and by how embodied cost is amortized over an assumed 5-year lifetime.
What would settle it
Run the same LLaMA workloads at batch size 1 on both GPUs while metering total system power at the wall (including CPU, DRAM, and cooling); if T4's per-prompt total energy is not below RTX6000 Ada's, the paper's central carbon conclusion fails.
Extended reading notes
Core claim
The central claim is that the older and slower T4 has higher energy efficiency than the newer and faster RTX6000 Ada when processing less compute-intensive requests (e.g., batch size 1), and that after including embodied carbon, strategically using older GPUs like T4 could effectively reduce total carbon emissions by amortizing the embodied carbon emissions of GPUs over time. The paper measures latency and GPU-only power (sampled every 100 ms with NVML) for LLaMA 1B, 3B, and 7B on both GPUs, splits serving into compute-bound prefill and memory-bound decode phases, and models total per-prompt carbon as $C_{\mathrm{prompt}} = E_{\mathrm{prompt}}\cdot CI + (t_{\mathrm{prompt}}/LT)\cdot C_{\mathrm{em}}$ for three grids (QC, CISO, and PACE). It reports that throughput-maximizing batch sizes are not energy-minimizing ones, and that embodied carbon can be up to 30.7% of total per-prompt carbon for RTX6000 Ada in a low-carbon grid, making older hardware attractive in such regions.
Load-bearing premise
The whole carbon ranking rests on measuring only GPU power; if cooling, CPU, memory, and power distribution overhead are counted, the older T4's longer execution time could turn its energy advantage into a disadvantage.
Editorial extensions
If this is right
- For latency-flexible workloads in low-carbon grids, datacenters can cut total carbon by routing some requests to older GPUs rather than always buying the newest generation.
- The batch size that maximizes throughput differs from the batch size that minimizes energy or carbon, so throughput-centric scheduling should not be assumed carbon-optimal.
- Extending GPU lifetime from 4 to 8 years shrinks the embodied share of per-token carbon, most visibly in low-carbon grids where embodied carbon already dominates.
- Carbon per token, not energy per token, should be the optimization target, since energy-minimal configurations are not always carbon-minimal once embodied emissions are included.
Reading between the lines
- A direct test: measure whole-system power (CPU, DRAM, cooling, PUE) for the same batch-size-1 prompts; if T4's longer runtime lifts system energy above RTX6000 Ada's, the carbon ranking could reverse, because this paper counts only GPU power.
- The prefill/decode split suggests a heterogeneous scheduling policy: run compute-heavy prefill on new GPUs and memory-bound decode on older ones, extending the paper's phase-level findings into a concrete system design.
- If embodied carbon were attributed to the whole server or the datacenter build rather than the GPU alone, the absolute numbers would change but the relative advantage of smaller, older chips would likely persist; this is a sensitivity check the paper does not run.
- For interactive serving where latency targets are strict, T4's 1.1-2.2x slowness at batch size 1 may rule it out despite the carbon benefit, so the result applies mainly to latency-flexible or batch workloads.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper presents a measurement study of LLaMA 1B/3B/7B inference on an RTX6000 Ada and an older T4 GPU across batch sizes from 1 to 64. It reports latency and GPU-only energy consumption, then combines these measurements with grid-specific carbon intensities (QC, CISO, PACE) and ACT-style embodied-carbon estimates to compute per-prompt and per-token operational, embodied, and 'total' carbon emissions. The central empirical finding is that the older T4 has lower GPU energy per prompt at batch size 1, and the paper argues that after amortizing embodied carbon, strategically using older GPUs like the T4 could reduce total carbon emissions, especially in low-carbon-intensity regions. The paper concludes with future directions on hardware reuse, carbon-aware scheduling, and sustainable LLM infrastructure.
Significance. If the headline finding survives system-level accounting, it is practically important: hardware generation would not be a reliable proxy for carbon efficiency, and the greenest GPU would depend on batch size, model size, grid carbon intensity, and hardware lifetime. The paper's measurements are transparent, the arithmetic in Equations (2)-(4) is internally consistent, and the use of three carbon-intensity regimes is a sensible way to separate operational from embodied contributions. The paper also makes a useful conceptual point that energy efficiency and carbon efficiency are not the same. The main limitation is that the 'total carbon' claim is currently computed from GPU-only power, so the central conclusion is conditional on non-GPU overhead being negligible.
major comments (3)
- [Section 2.1, Eq. (4)] The headline claim in the abstract and the Introduction that 'strategically using older GPUs like T4 could effectively reduce total carbon emissions' is not yet supported, because Eq. (4) labels GPU-only operational energy as 'total carbon emission.' Section 2.1 explicitly says 'this study focuses on GPU power consumption,' and Eq. (1) uses NVML GPU power only. For the 7B model at batch size 1, the paper reports that T4's GPU energy is 20% lower but its latency is 2.2x higher than RTX6000 Ada's. Under those numbers, any fixed non-GPU power (CPU, DRAM, cooling, PSU losses, PUE overhead) exceeding roughly one sixth of the RTX6000 Ada's average GPU power makes T4's system-level carbon per prompt higher than Ada's. That is a low threshold for a real serving node. Please either add node-level energy measurements or a defensible PUE/overhead model, or relabel the metric as 'GPU-power-based operational carbon plus embodied carbon' and soften the total-carbon claims accordingly.
- [Section 2.2] The empirical characterization reports median latency and average power but gives no number of trials, no variance, and no statistical significance. The batch-size-1 energy advantage of T4 over RTX6000 Ada is 28% for the 1B model and 20% for the 7B model, while the 3B comparison is a 1.4x disadvantage; these are small margins that could reverse under measurement noise, thermal variation, or prompt heterogeneity. Please report run counts, error bars, and ideally confidence intervals for the latency and energy values that underlie the main comparisons.
- [Section 3.1 and Section 3.4, Eq. (3)] The embodied-carbon analysis assumes a single fixed 5-year lifetime for both GPUs, and the sensitivity study in Section 3.4 sweeps only the T4's lifetime while keeping RTX6000 Ada's at 5 years. Since the total-carbon comparison between older and newer GPUs depends directly on the lifetime ratio, the conclusion that older GPUs reduce total carbon is conditional on an assumed ratio that is plausible but not demonstrated. The paper should show how the batch-size-1 total-carbon ordering changes when both lifetimes vary over a realistic range, not just T4's lifetime.
minor comments (5)
- [Figures 5 and 6] The captions say the figures are 'under the CISO grid,' but the body text says 'We use the QC's CI value' and the figure legends label the operational component as 'Operational (QC).' Please align the captions, legends, and text.
- [Section 2.1] The number of prompts used in the evaluation is not reported, only that prompts generating more than 150 tokens are considered. Reporting the dataset size and the distribution of prompt lengths would help assess the representativeness of the median latency and average power.
- [Table 1] The technology node for RTX6000 Ada is listed as 5 nm, but the actual process is NVIDIA's 4N custom node; please use the vendor-specified process name or add a citation.
- [Section 2.2] The abbreviation 'OOM' is used in Figure 1 but is not defined at first use; please spell out 'out of memory' in the text or caption.
- [References] Reference [34] is a blog citation for ChatGPT's carbon per query; a primary or peer-reviewed source would be more appropriate for a quantitative claim in the introduction.
Circularity Check
No circularity: carbon results are arithmetic compositions of measured energy/time, external carbon intensities, and ACT embodied values.
full rationale
The paper's derivation chain is a transparent accounting model. Energy consumption is measured directly with NVML (Eq. 1: E_prompt = P_prompt * t_prompt). Operational carbon is the product of that measured energy and externally sourced grid carbon intensities (Eq. 2). Embodied carbon is the execution-time-weighted fraction of ACT-derived chip-area/memory embodied values (Eq. 3), and total carbon is the sum (Eq. 4). No parameter is fitted to the paper's conclusions, and no 'prediction' is derived from the result it is supposed to establish. The finding that T4 can be more energy-efficient at batch size 1 is an empirical measurement reported in Section 2.2, not an artifact of the model. The carbon conclusions are logical consequences of multiplying measured quantities by stated external factors. The only notable caveat — that the study focuses on GPU power rather than full node power — is a scope limitation and a possible correctness risk, not a circularity: the equations honestly state what is included. The paper does not rely on self-citations to justify its central premise, and the embodied-carbon values are taken from an independent architectural carbon modeling tool (ACT) and compared to another independent study. Therefore the analysis is self-contained as an accounting model and warrants a circularity score of 0.
Assumptions & free parameters
free parameters (1)
- GPU lifetime assumption (LT) =
5 years
assumptions (4)
- domain assumption GPU power consumption is the only significant contributor to LLM serving energy.
- domain assumption ACT embodied carbon estimates based on chip area and memory size are accurate for these two GPUs.
- domain assumption Static annual average carbon intensities per region capture operational emissions.
- domain assumption Alpaca prompts generating more than 150 tokens represent LLM serving workloads.
Cite this review
Pith. "Pith review of Towards Sustainable Large Language Model Serving." pith.science (2026). https://pith.science/paper/NOMIZW2G
@misc{pith2026250101990,
author = {Pith},
title = {Pith review of: Towards Sustainable Large Language Model Serving},
year = {2026},
howpublished = {\url{https://pith.science/paper/NOMIZW2G}},
note = {Machine review of arXiv:2501.01990}
}
read the original abstract
In this work, we study LLMs from a carbon emission perspective, addressing both operational and embodied emissions, and paving the way for sustainable LLM serving. We characterize the performance and energy of LLaMA with 1B, 3B, and 7B parameters using two Nvidia GPU types, a latest-generation RTX6000 Ada and an older-generation T4. We analytically model operational carbon emissions based on energy consumption and carbon intensities from three grid regions -- each representing a different energy source mix, and embodied carbon emissions based on chip area and memory size. Our characterization and modeling provide us with an in-depth understanding of the performance, energy, and carbon emissions of LLM serving. Our findings highlight the potential for optimizing sustainable LLM serving systems by considering both operational and embodied carbon emissions simultaneously.
Figures
Figures from the paper (3 more)
Reference graph
Works this paper leans on
- [1]
-
[2]
Reducing the carbon impact of generative AI inference (today and in 2035)
Andrew A Chien, Liuzixuan Lin, Hai Nguyen, Varsha Rao, Tristan Sharma, and Rajini Wijayawardana. Reducing the carbon impact of generative AI inference (today and in 2035). In Proceedings of the 2nd Workshop on Sustainable Computer Systems (HotCarbon), pages 1–7, 2023
work page 2023
-
[3]
Aakanksha Chowdhery, Sharan Narang, Jacob Devlin, Maarten Bosma, Gaurav Mishra, Adam Roberts, Paul Barham, Hyung Won Chung, Charles Sutton, Sebas- tian Gehrmann, Parker Schuh, Kensen Shi, Sasha Tsvyashchenko, Joshua Maynez, Abhishek Rao, Parker Barnes, Yi Tay, Noam Shazeer, Vinodkumar Prabhakaran, Emily Reif, Nan Du, Ben Hutchinson, Reiner Pope, James Bra...
arXiv 2022
-
[4]
Electricity Maps ApS. Electricity maps. https://app.electricitymaps.com/, 2024
work page 2024
-
[5]
Fine- tuning giant neural networks on commodity hardware with automatic pipeline model parallelism
Saar Eliad, Ido Hakimi, Alon De Jagger, Mark Silberstein, and Assaf Schuster. Fine- tuning giant neural networks on commodity hardware with automatic pipeline model parallelism. In USENIX Annual Technical Conference (ATC), 2021
work page 2021
-
[6]
LLMCarbon: Modeling the end-to-end carbon footprint of large language models
Ahmad Faiz, Sotaro Kaneda, Ruhan Wang, Rita Chukwunyere Osi, Prateek Sharma, Fan Chen, and Lei Jiang. LLMCarbon: Modeling the end-to-end carbon footprint of large language models. In The Twelfth International Conference on Learning Representations (ICLR), 2024
work page 2024
-
[7]
Bin Gao, Zhuomin He, Puru Sharma, Qingxuan Kang, Djordje Jevdjic, Junbo Deng, Xingkun Yang, Zhou Yu, and Pengfei Zuo. AttentionStore: Cost-effective attention reuse across multi-turn conversations in large language model serving. arXiv preprint arXiv:2403.19708, 2024
arXiv 2024
-
[8]
Accelerate AI development with Google cloud TPUs
Google. Accelerate AI development with Google cloud TPUs. https://cloud. google.com/tpu
Show all 40 references
-
[9]
Why your internet habits are not as clean as you think
Sarah Griffiths. Why your internet habits are not as clean as you think. https://www.bbc.com/future/article/20200305-why-your-internet-habits- are-not-as-clean-as-you-think, 2020
2020
-
[10]
Lee, David Brooks, and Carole-Jean Wu
Udit Gupta, Mariam Elgamal, Gage Hills, Gu-Yeon Wei, Hsien-Hsin S. Lee, David Brooks, and Carole-Jean Wu. ACT: Designing sustainable computer systems with an architectural carbon modeling tool. In Proceedings of the 49th Annual International Symposium on Computer Architecture ...
2022
-
[11]
Small language models fine-tuned to coordinate larger language models improve complex reasoning
Gurusha Juneja, Subhabrata Dutta, Soumen Chakrabarti, Sunny Manchanda, and Tanmoy Chakraborty. Small language models fine-tuned to coordinate larger language models improve complex reasoning. arXiv preprint arXiv:2310.18338, 2024
-
[12]
Fast inference from transform- ers via speculative decoding
Yaniv Leviathan, Matan Kalman, and Yossi Matias. Fast inference from transform- ers via speculative decoding. In Proceedings of the 40th International Conference on Machine Learning (ICML) , 2023. Towards Sustainable Large Language Model Serving HotCarbon’24, July 9, 2024, San...
2023
-
[13]
Toward sustainable HPC: Carbon footprint estimation and environmental implications of HPC systems
Baolin Li, Rohan Basu Roy, Daniel Wang, Siddharth Samsi, Vijay Gadepally, and Devesh Tiwari. Toward sustainable HPC: Carbon footprint estimation and environmental implications of HPC systems. In Proceedings of the International Conference for High Performance Computing, Networ...
2023
-
[14]
Is your code generated by ChatGPT really correct? rigorous evaluation of large language models for code generation
Jiawei Liu, Chunqiu Steven Xia, Yuyao Wang, and Lingming Zhang. Is your code generated by ChatGPT really correct? rigorous evaluation of large language models for code generation. Advances in Neural Information Processing Systems (NeurIPS), 36, 2024
2024
-
[15]
Counting carbon: A survey of factors influencing the emissions of machine learning
Alexandra Sasha Luccioni and Alex Hernandez-Garcia. Counting carbon: A survey of factors influencing the emissions of machine learning. arXiv preprint arXiv:2302.08476, 2023
2023 arXiv
-
[16]
Estimating the carbon footprint of BLOOM, A 176B parameter language model
Alexandra Sasha Luccioni, Sylvain Viguier, and Anne-Laure Ligozat. Estimating the carbon footprint of BLOOM, A 176B parameter language model. J. Mach. Learn. Res., 24(1), mar 2024
2024
-
[17]
Bringing carbon awareness to multi-cloud application delivery
Diptyaroop Maji, Ben Pfaff, Vipin P R, Rajagopal Sreenivasan, Victor Firoiu, Sreeram Iyer, Colleen Josephson, Zhelong Pan, and Ramesh K Sitaraman. Bringing carbon awareness to multi-cloud application delivery. In Proceedings of the 2nd Workshop on Sustainable Computer Systems ...
2023
-
[18]
Sitaraman
Diptyaroop Maji, Prashant Shenoy, and Ramesh K. Sitaraman. CarbonCast: Multi-day forecasting of grid carbon intensity. In Proceedings of the 9th ACM International Conference on Systems for Energy-Efficient Buildings, Cities, and Transportation (BuildSys), 2022
2022
-
[19]
Sitaraman, and Prashant Shenoy
Diptyaroop Maji, Ramesh K. Sitaraman, and Prashant Shenoy. DACF: Day- ahead carbon intensity forecasting of power grids using machine learning. In Proceedings of the Thirteenth ACM International Conference on Future Energy Systems (e-Energy), e-Energy ’22, 2022
2022
-
[20]
MTIA v1: Meta’s first-generation AI inference accelerator
Meta. MTIA v1: Meta’s first-generation AI inference accelerator. https://ai.meta. com/blog/meta-training-inference-accelerator-AI-MTIA/, 2023
2023
-
[21]
NVIDIA HGX AI Supercomputer
Nvidia. NVIDIA HGX AI Supercomputer. https://www.nvidia.com/en-us/data- center/hgx/, 2024
2024
-
[22]
NVIDIA management library (NVML)
Nvidia. NVIDIA management library (NVML). https://developer.nvidia.com/ management-library-nvml, 2024
2024
-
[23]
Ashraf, Christian Engelmann, Mallikarjun Shankar, and James H
George Ostrouchov, Don Maxwell, Rizwan A. Ashraf, Christian Engelmann, Mallikarjun Shankar, and James H. Rogers. GPU lifetimes on titan supercomputer: Survival analysis and reliability. In Proceedings of the International Conference for High Performance Computing, Networking, ...
2020
-
[24]
Splitwise improves GPU usage by splitting LLM inference phases
Pratyush Patel, Esha Choukse, Chaojie Zhang, Íñigo Goiri, Aashaka Shah, Saeed Maleki, and Ricardo Bianchini. Splitwise improves GPU usage by splitting LLM inference phases. In International Symposium on Computer Architecture (ISCA) , 2024
2024
-
[25]
So, Maud Texier, and Jeff Dean
David Patterson, Joseph Gonzalez, Urs Hölzle, Quoc Le, Chen Liang, Lluis-Miquel Munguia, Daniel Rothchild, David R. So, Maud Texier, and Jeff Dean. The carbon footprint of machine learning training will plateau, then shrink. Computer, 2022
2022
-
[26]
HuggingGPT: Solving AI tasks with ChatGPT and its friends in hugging face
Yongliang Shen, Kaitao Song, Xu Tan, Dongsheng Li, Weiming Lu, and Yueting Zhuang. HuggingGPT: Solving AI tasks with ChatGPT and its friends in hugging face. Advances in Neural Information Processing Systems (NeurIPS) , 36, 2024
2024
-
[27]
PowerInfer: Fast large language model serving with a consumer-grade GPU
Yixin Song, Zeyu Mi, Haotong Xie, and Haibo Chen. PowerInfer: Fast large language model serving with a consumer-grade GPU. arXiv preprint arXiv:2312.12456, 2023
2023 arXiv
-
[28]
Hashimoto
Rohan Taori, Ishaan Gulrajani, Tianyi Zhang, Yann Dubois, Xuechen Li, Car- los Guestrin, Percy Liang, and Tatsunori B. Hashimoto. Stanford Alpaca: An instruction-following LLaMA model. https://github.com/tatsu-lab/stanford_ alpaca, 2023
2023
-
[29]
NVIDIA Tesla T4
TechPowerUP. NVIDIA Tesla T4. https://www.techpowerup.com/gpu-specs/ tesla-t4.c3316/, 2018
2018
-
[30]
NVIDIA RTX 6000 Ada Generation
TechPowerUP. NVIDIA RTX 6000 Ada Generation. https://www.techpowerup. com/gpu-specs/rtx-6000-ada-generation.c3933/, 2023
2023
-
[31]
LLaMA: Open and efficient foundation language models
Hugo Touvron, Thibaut Lavril, Gautier Izacard, Xavier Martinet, Marie-Anne Lachaux, Timothée Lacroix, Baptiste Rozière, Naman Goyal, Eric Hambro, Faisal Azhar, Aurelien Rodriguez, Armand Joulin, Edouard Grave, and Guillaume Lam- ple. LLaMA: Open and efficient foundation langua...
2023 arXiv
-
[32]
FreshLLMs: Refreshing large lan- guage models with search engine augmentation
Tu Vu, Mohit Iyyer, Xuezhi Wang, Noah Constant, Jerry Wei, Jason Wei, Chris Tar, Yun-Hsuan Sung, Denny Zhou, Quoc Le, et al. FreshLLMs: Refreshing large lan- guage models with search engine augmentation. arXiv preprint arXiv:2310.03214, 2023
-
[33]
Peeling back the carbon curtain: Carbon optimization challenges in cloud computing
Jaylen Wang, Udit Gupta, and Akshitha Sriraman. Peeling back the carbon curtain: Carbon optimization challenges in cloud computing. In Workshop on Sustainable Computer Systems (HotCarbon) , 2023
2023
-
[34]
Gen AI’s environmental ledger: A closer look at the carbon footprint of ChatGPT
Vinnie Wong. Gen AI’s environmental ledger: A closer look at the carbon footprint of ChatGPT. https://piktochart.com/blog/carbon-footprint-of-chatgpt/, 2023
2023
-
[35]
Small models are valuable plug-ins for large language models
Canwen Xu, Yichong Xu, Shuohang Wang, Yang Liu, Chenguang Zhu, and Julian McAuley. Small models are valuable plug-ins for large language models. arXiv preprint arXiv:2305.08848, 2023
2023 arXiv
-
[36]
ASPEN: High-throughput LoRA fine-tuning of large language models with a single GPU
Zhengmao Ye, Dengchun Li, Jingqi Tian, Tingfeng Lan, Jie Zuo, Lei Duan, Hui Lu, Yexi Jiang, Jian Sha, Ke Zhang, and Mingjie Tang. ASPEN: High-throughput LoRA fine-tuning of large language models with a single GPU. arXiv preprint arXiv:2312.02515, 2023
2023 arXiv
-
[37]
Patil, Naman Jain, Sheng Shen, Matei Zaharia, Ion Stoica, and Joseph E
Tianjun Zhang, Shishir G. Patil, Naman Jain, Sheng Shen, Matei Zaharia, Ion Stoica, and Joseph E. Gonzalez. RAFT: Adapting language model to domain specific RAG. arXiv preprint arXiv:2403.10131, 2024
2024 arXiv
-
[38]
A GNN-based day ahead carbon intensity forecasting model for cross-border power grids
Xiaoyang Zhang and Dan Wang. A GNN-based day ahead carbon intensity forecasting model for cross-border power grids. In Proceedings of the 14th ACM International Conference on Future Energy Systems (e-Energy) , e-Energy ’23, 2023
2023
-
[39]
Embodied carbon account- ing through spatial-temporal embodied carbon models
Xiaoyang Zhang, Yijie Yang, and Dan Wang. Embodied carbon account- ing through spatial-temporal embodied carbon models. arXiv preprint arXiv:2312.06364, 2023
2023 arXiv
-
[40]
DistServe: Disaggregating prefill and decoding for goodput- optimized large language model serving
Yinmin Zhong, Shengyu Liu, Junda Chen, Jianbo Hu, Yibo Zhu, Xuanzhe Liu, Xin Jin, and Hao Zhang. DistServe: Disaggregating prefill and decoding for goodput- optimized large language model serving. arXiv preprint arXiv:2401.09670, 2024
2024 arXiv
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