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7622b45921
Summary: pickNodeBidirectional tried to compare the best top candidate and the best bottom candidate by examining TopCand.Reason and BotCand.Reason. This is unsound because, after calling pickNodeFromQueue, Cand.Reason does not reflect the most important reason why Cand was chosen. Rather it reflects the most recent reason why it beat some other potential candidate, which could have been for some low priority tie breaker reason. I have seen this cause problems where TopCand is a good candidate, but because TopCand.Reason is ORDER (which is very low priority) it is repeatedly ignored in favour of a mediocre BotCand. This is not how bidirectional scheduling is supposed to work. To fix this I changed the code to always compare TopCand and BotCand directly, like the generic implementation of pickNodeBidirectional does. This removes some uncommented AMDGPU-specific logic; if this logic turns out to be important then perhaps it could be moved into an override of tryCandidate instead. Graphics shader benchmarking on gfx10 shows a lot more positive than negative effects from this change. Reviewers: arsenm, tstellar, rampitec, kzhuravl, vpykhtin, dstuttard, tpr, atrick, MatzeB Subscribers: jvesely, wdng, nhaehnle, yaxunl, t-tye, hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D68338 |
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