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Fsdp ptd #1085

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Fsdp ptd #1085

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ruanslv
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@ruanslv ruanslv commented Sep 27, 2022

  • Disable prefetching (re-enable 2 PG backward)
  • Check queue at the beginning of all-gather
  • Update queue after a free event

@facebook-github-bot facebook-github-bot added the CLA Signed This label is managed by the Facebook bot. Authors need to sign the CLA before a PR can be reviewed. label Sep 27, 2022
@min-xu-ai
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Just curious, is this PR trying to the "limiter" thing as PTD's fsdp here?

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ruanslv commented Sep 29, 2022

Yes exactly. events[-1].synchronize() doesn't seem to be working as is, however.

@cyugao cyugao marked this pull request as ready for review October 7, 2022 22:05
@cyugao cyugao marked this pull request as draft October 7, 2022 22:08
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awgu commented Oct 12, 2022

As a heads up, I made a small change to improve the rate limiter: pytorch/pytorch#86165

It is actually more performant to only dequeue and synchronize one event compared to flushing the queue. The overhead to consider is not from the CPU dequeueing and calling .synchronize() but rather the time taken to block the CPU thread during .synchronize(). Dequeueing only one reduces gaps in the communication stream, as can be seen in the PR summary. Under this new approach, a limit of 2 makes sense because it is the minimal limit to still achieve overlap.

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