Fix NCCL test hang #9367
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Fix NCCL test hang #9367
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trivialfis
reviewed
Jul 6, 2023
| * because NCCL kernels are blocking. The extra CUDA stream synchronization makes sure that the | ||
| * NCCL kernels are caught up, thus avoiding the deadlock. | ||
| */ | ||
| explicit NcclDeviceCommunicator(int device_ordinal, bool needs_sync = false); |
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Can we avoid the default parameter? Would be better if we have a clear reference to who's asking for sync and who is not.
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You mean per-thread default stream? I'm not sure it'll help here. The issue seems to be creating multiple NCCL communicators in the same process and mixing NCCL kernels with ours. |
trivialfis
approved these changes
Jul 7, 2023
|
Thank you for the quick fix! |
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The NCCL communicator tests sometimes hang because NCCL kernels are blocking, and mixing with
LaunchNcalls might cause a deadlock. Synchronizing on the stream beforeLaunchNseems to fix this issue.