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Investigate why crossgen works slower with TieredCompilation/PGO #83112
Description
I was measuring crossgen2.exe -O SPC.dll (actually, the exact command we use for build Clr.NativeCoreLib -c Release) and noticed a few problems:
| Mode | Time to prejit SPC.dll, seconds |
|---|---|
| TC=1 (Default) | 4.81 |
| TC=0 | 4.25 |
| TC=1, CCDelayMS=0 | 3.78 |
| TC=1, PGO=1 | 5.29 |
| TC=1, PGO=1, CCDelayMS=0 | 3.93 |
Legend:
TC-DOTNET_TieredCompilation(1by default)PGO-DOTNET_TieredPGO(0by default)CCDelayMS-DOTNET_TC_CallCountThreshold(100by default)
The difference is quite noticeable so worth investigating - numbers are quite stable across multiple runs.
Judging by the effect from DOTNET_TC_CallCountThreshold we're having some contention for call counting stub installation/promotion to tier1.
Activity
EgorBo commentedon Mar 7, 2023
Fun-fact:
DOTNET_TC_CallCountingDelayMs=1makesTC=1 (default)faster thanTC=0. So apparently there is a huge contention to install call counting stubsEgorBo commentedon Mar 8, 2023
cc @noahfalk @kouvel
kunalspathak commentedon Jul 24, 2023
From https://pvscmdupload.blob.core.windows.net/reports/allTestHistory%2frefs%2fheads%2fmain_x64_Windows%2010.0.18362_RunKind%3dcrossgen_scenarios%2fCrossgen2%20Throughput%20-%20Single%20-%20System.Private.CoreLib.html
The regression is seen after enabling dynamic PGO in #86225
@davidwrighton @mangod9
AndyAyersMS commentedon Jul 24, 2023
As mentioned offline we also ought to start measuring with the NAOT'd crossgen2.
MichalStrehovsky commentedon Jul 27, 2023
#89489 disabled tiering to work around (matching the workaround used in ILC already) so if we still do TP measurements in the non-shipping configuration of crossgen2, there's going to be an improvement.