[Pipelining] Add debug logs for batch p2p ops

[wconstab]

Stack from ghstack (oldest at bottom):

• [Pipelining] Clean up function names in 1f1b schedule #126582
• -> [Pipelining] Add debug logs for batch p2p ops #126539

logs from torchtitan:

cc @mrshenli @pritamdamania87 @zhaojuanmao @satgera @gqchen @aazzolini @osalpekar @jiayisuse @H-Huang @kwen2501 @awgu @penguinwu @fegin @XilunWu @wanchaol @fduwjj @wz337 @tianyu-l @yf225 @chauhang @d4l3k

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/126539

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❌ 1 New Failure, 1 Unrelated Failure

As of commit 60a400d with merge base failed to retrieve merge base, please contact dev infra:

NEW FAILURE - The following job has failed:

• BC Lint / bc_linter (gh)
  Process completed with exit code 1.

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• trunk / win-vs2019-cpu-py3 / test (default, 1, 3, windows.4xlarge.nonephemeral) (gh) (similar failure)
  Process completed with exit code 1.

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[H-Huang]

LGTM

[kwen2501]

lgtm

[wconstab]

@pytorchbot merge -f "intentional BC change for newly added (as yet unreleased) API"

[pytorchmergebot]

Merge started

Your change will be merged immediately since you used the force (-f) flag, bypassing any CI checks (ETA: 1-5 minutes). Please use -f as last resort and instead consider -i/--ignore-current to continue the merge ignoring current failures. This will allow currently pending tests to finish and report signal before the merge.

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