[PATCH] D82123: [PGO] Add a functionality to always instrument the func entry BB

[Wei Mi via Phabricator via llvm-commits]

wmi added a comment.

I tried it on an internal benchmark.

base: head of trunk
exp:  pgo-instrument-entry=true, atomic-first-counter=false
qps of Instrumented binary run: 344.63 vs 340.56
optimized binary run: qps had no significant change in 6 runs. latency had ~0.1% regression in 3 runs and no regression in other 3 runs.

base: head of trunk
exp:  pgo-instrument-entry=true, atomic-first-counter=true
qps of Instrumented binary run: 342.53 vs 265.58
optimized binary run: qps had no significant change in 2 runs, and had ~0.11% improvement in 4 runs. latency had ~0.35% improvement in 6 runs.

The test showed always inserting counter in the entry block had minor impact on instrumented binary and optimized binary runs. Using atomic entry counter could improve profile quality but significantly slowdown instrument binary.


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  https://reviews.llvm.org/D82123/new/

https://reviews.llvm.org/D82123