find optimal number of workers

[dimapihtar]

What does this PR do ?

Adds a feature to find optimal number of workers for data preprocessing. Bigger number of workers doesn't always mean faster data processing. This PR allows to find the most optimal number of workers in terms of their data processing performance. Script will run a few short data prep runs with different number of workers and then compare their performance.

Example:

python tools/preprocess_data.py \
    --input data.jsonl \
    --output-prefix processed_data \
    --tokenizer-type HuggingFaceTokenizer \
    --tokenizer-model /path/to/tokenizer.model \
    --workers 8 \
    --find-optimal-num-workers \
    --workers-to-check 4 8 16 32 \
    --performance-dir /path/to/save/perf/results \
    --max-documents 50000

Output example:

-----------------------------------
Performance results (fastest → slowest):
1. 16 workers → avg. docs/s: 9606.6476
2. 32 workers → avg. docs/s: 9275.3284
3. 8 workers → avg. docs/s: 9151.9280
4. 4 workers → avg. docs/s: 6391.3819

-----------------------------------
The most optimal num of workers is 16 with avg. preprocessed docs/s: 9606.6476.
-----------------------------------

PR also adds related documentation and unit test case.

⚠️ For major changes (either in lines of code or in its impact), please make sure to first share a design doc with the team. If you're unsure what's the best way to do so, contact the @mcore-oncall.

Contribution process

flowchart LR
    A[Pre-checks] --> B[PR Tests]
    subgraph Code Review/Approval
        C1[Expert Review] --> C2[Final Review]
    end
    B --> C1
    C2 --> D[Merge]

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Pre-checks

• I want this PR in a versioned release and have added the appropriate Milestone (e.g., Core 0.8)
• I have added relevant unit tests
• I have added relevant functional tests
• I have added proper typing to my code Typing guidelines
• I have added relevant documentation
• I have run the autoformatter.sh on my PR

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Final Review might get declined if these requirements are not fulfilled.

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If this PR also needs to be merged into core_r* release branches, after this PR has been merged, select Cherry-pick to open a new PR into the release branch.

For MRs into `dev` branch

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MRs are mergable after one approval by either eharper@nvidia.com or zijiey@nvidia.com.

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[copy-pr-bot]

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[dimapihtar]

/ok to test f1c2631

[Phlip79]

We are changing our review process and marking all open, unlabeled PRs as draft. This change will go in effect starting once #3659 is merged.

Moving forward, all PRs will be required to start as draft PRs. If you wish to get your PR merged, mark your PR as “Ready for review”. Read more about the new process at submit.md.

[dimapihtar]

/ok to test b20b314

[dimapihtar]

/ok to test 2827707

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/23045065317