Training

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Overview

We need to model the environmental impact of the computation for the trained model. The training costs of genAI models are often disclosed in some form. These costs must be normalized and then amortized across the expected use-life of the model.

The key components of the training cost of the model include:

• The operational energy used to train the final model
• The operational energy used to train intermediate and preliminary models
• The embodied emissions from the cluster used to train all models, including hardware reserved but not actively deployed
• (Allocated emissions from generation of the training and test data)
• (Allocated operational and embodied emissions of development and testing infrastructure)

Carbon Emissions and Large Neural Network Training includes a table that shows the impact of changing the model, the datacenter, the gpu, and the energy grid in training a model:

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Disclosure of training costs

To fully assess environmental impact, model developers should disclose the technical infrastructure used for training and how this infrastructure was engaged during the training process.

Infrastructure data:

• Training cluster details
• Training cluster location(s) - if hosted in a cloud, which region(s)

Operational data:

• Total reserved/owned wall clock time for intermediate and final model training
• CPU utilization % for model training
• GPU hours for intermediate model training
• GPU hours for final model training

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Example disclosure

As an example of a relatively complete disclosure, see Sasha Luccioni, Sylvain Viguier, and Anne-Laure Ligozat. 2022. Estimating the carbon footprint of Bloom, a 176B parameter language model.: “We estimate that BLOOM’s final training emitted approximately 24.7 tonnes of CO2eq if we consider only the dynamic power consumption, and 50.5 tonnes if we account for all processes ranging from equipment manufacturing to energy-based operational consumption.”

Infrastructure data

Training data

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Normalization of disclosed data

When disclosed data is not present or not complete, we need to use predictive or heuristic data to fill in the gaps.

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Example normalization: BLOOM 176B

The BLOOM paper includes most of the required parameters for carbon emissions. However, it does not include data for water consumption. We use the fallbacks for the missing data points in the calculations below.

Some assumptions:

• The 35.8 tons of CO2 for the intermediate models implies proportional reservation and usage as the final model. The total emissions for all models is then 35.8+24.69 tons, so we can extrapolate by a factor of 2.45x.

Normalized training data

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Calculation of carbon emissions

To calculate CO2 emissions, we use the Software Carbon Intensity formula. We need a few data points:

• The usage energy per GPU hour for the cluster
• The embodied emissions per reserved hour for the cluster
• The carbon intensity of the grid in the training location(s) during the training time period

The training emissions will be:

Total emissions = (embodied emissions) + (usage emissions)

Embodied emissions = (cluster embodied emissions per hour) x (training time)

Usage emissions = (usage energy per GPU-hour) x (total GPU hours) x (average grid intensity during training)

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Example carbon calculation

For the final BLOOM model described above:

Modeling the cluster produces:

E(gpu-h) = (.428 kW) x (1.1)
         = .471 kW

EmbEm(h) = ((384 GPUs) x (318 kgCO2e/GPU) +
             (48 servers) x (2500 kgCO2e/server))
            / (4 years)
            / (8760 hours/year)
            / (95% utilization)
         = 7.27 kgCO2e/hour

Training emissions based on the normalized data:

EmbEm(training) = (7.27 kgCO2e/h) x (289 d) x (24 h/d)
                = 50,425 kgCO2e

OpEm(training)  = (.471 kW) x (2653326 h) x (57 kgCO2/kWh)
                = 71,234 kgCO2e

Em(training)    = 121,659 mtCO2e

Note that this calculation produces a higher estimate for embodied emissions on the final model (20.6 mtCO2e) than the 11.2 mtCO2e in the BLOOM paper referenced above for three reasons. First, the embodied emissions for the A100 are higher based on a more detailed paper. Second, we use a shorter use life as hardware efficiency is increasing extremely quickly in the AI space and these servers will be obsolete more quickly than general-purpose servers. Third, we use a higher utilization number based on increased demand for GPUs.

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Calculation of water impact

The water impact of training includes:

• The water consumed to cool the servers during the training period (using the “water utilization efficiency” or WUE of the datacenter)
• The water consumed to produce the electricity used by the servers
• The water consumed to produce the chips and servers

The water impact is calculated by:

Datacenter water consumption = (Usage energy per GPU) x (total GPU hours) x (datacenter WUE)
Electricity water consumption = (Usage energy per GPU) x (total GPU hours) x (electricity WUE)
Manufacturing water consumption = (Cluster embodied H2O per hour) x (total training hours)

TODO - update above to use cluster metrics and include PUE for the scope 2 number

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Example of water impact calculation for BLOOM 176B

Modeling the cluster produces:

EmbH2O(h) = ((384 GPUs) x (412 L/GPU))
            / (4 years)
            / (8760 hours/year)
            / (95% utilization)
          = 4.75 L/h

This produces:

Datacenter H2O = (0.428 kW) x (2653326 hours) x 1.8 L/kWh = 2,044 kL
Electricity H2O = (0.428 kW) x (2653326 hours) x 3.67 L/kWh = 4,168 kL
Manufacturing H2O = (2832 h) x (4.75 L/h) = 13.5 kL

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Amortization of impact across use life

A general-purpose model is likely to be used heavily for a period of time then made obsolete by newer models that are more effective and/or more efficient. Specialized models may have longer use lives. Open source models enable fine tuning that will create stickiness for ongoing use.

Each model should have a projected use life and track the actual and projected number of inferences for each month during that use life. As actual inference numbers are calculated each month, the projections for the remaining use life should be updated. Since actual inference numbers are sensitive, the model developer could publish the percent of amortized training cost remaining.

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Amortization schedule tables

Initial amortization schedule

PI means the total projected inferences N means the total use life in months TC means the total training cost

Amortization schedule after month 1

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Open Questions

• How to estimate projected inferences and use life for a new model (vs an upgrade)
• How to estimate actual inferences for a closed model that doesn’t disclose usage
• How to estimate actual inferences for an open source model like LLAMA where the use is not happening in a centralized fashion

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Example of amortization

Traffic to ChatGPT was relatively flat from April 2023 to April 2024, averaging around 50M visits a day. Assuming 5 queries per visit and 925 inferences per query, this would represent 7T inferences per month.

With the impending release of GPT-4o, a reasonable projection would be that traffic would continue at the same rate, and that the model lifecycle would be around a year given the 14-month gap between GPT-4 and GPT-4o.

The initial amortization schedule would look like:

What actually happened was that thanks to the new model, traffic to chatgpt.com increased by 55% in June 2024 after the release of GPT-4o.

The spike in traffic means that the model was effectively overbilled in month 1, making the projected training cost per inference much lower thanks to higher projected volume and the lower remaining training cost.