fix(dp): wait forward before gather_req - #1506
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The next infer thread may launch DP all-gathers before the previous overlap-stream forward finishes, causing NCCL to overlap with DeepEP/MTP kernels. Make the current stream wait before starting DP collectives while preserving overlap for request preparation.
WANDY666
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Summary
Root cause
With overlap enabled, the previous infer thread can release forward before its GPU work finishes. The next infer-loop iteration may then enqueue DP all-gathers on the current stream while the prior DeepEP/MTP kernels are still running. Adding an explicit stream dependency restores the required ordering.
This PR isolates the fix from
d5b04bfonto the latestmain; the resulting commit isb98f6802.Testing
git diff --checkpasses.