Disable tiered compilation in the compiler#80154
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VS performance data indicated that tiered compilation was negatively impacting compiler throughput. Using the [replay tool](https://github.com/dotnet/roslyn/tree/main/src/Tools/Replay) I measured the impact of R2R, Tier and Tier PGO on a number of scenarios and got the following data: | Scenario | R2R | Tier | Tier PGO | Total Compilations | Iterations | Avg Time | | ---------- | --- | ---- | -------- | ------------------ | ---------- | -------- | | complog | Off | Off | Off | 11 | 5 | 0:04 | | complog | Off | On | On | 11 | 5 | 0:03 | | CSharp.Semantics | Off | Off | Off | 94 | 5 | 0:05 | | CSharp.Semantics | Off | On | On | 94 | 5 | 0:08 | | CSharp.Semantics | On | Off | Off | 94 | 5 | 0:05 | | CSharp.Semantics | On | On | On | 94 | 5 | 0:09 | | Compilers.slnf | Off | Off | Off | 510 | 3 | 1:02 | | Compilers.slnf | Off | On | On | 510 | 3 | 1:28 | | Compilers.slnf | On | Off | Off | 510 | 3 | 0:56 | | Compilers.slnf | On | On | Off | 510 | 3 | 1:08 | | Compilers.slnf | On | On | On | 510 | 3 | 1:30 | | Roslyn.sln | Off | Off | Off | 1461 | 3 | 1:02 | | Roslyn.sln | Off | On | Off | 1461 | 3 | 1:30 | | Roslyn.sln | On | Off | Off | 1461 | 3 | 0:58 | | Roslyn.sln | On | On | On | 1461 | 3 | 1:28 | | Roslyn.sln | On | On | Off | 1461 | 3 | 1:11 | This strongly indicates that tiering is having a negative impact on compiler throughput. For now we're going to disable it and measure the impact in the VS perf labs. Note: Used the `%DOTNET_TieredCompilation%` and `%DOTNET_TieredPGO%` to control `Tier` and `TierPGO` respectively
JoeRobich
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Sep 5, 2025
AlekseyTs
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RikkiGibson
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mainly want @akhera99 to have heads up about this since we want to keep an eye on any changes that might occur in the resulting insertion.
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VS performance data indicated that tiered compilation was negatively impacting compiler throughput. Using the
replay tool I measured the impact of R2R, Tier and Tier PGO on a number of scenarios and got the following data:
This strongly indicates that tiering is having a negative impact on compiler throughput. For now we're going to disable it and measure the impact in the VS perf labs.
Note:
Used the
%DOTNET_TieredCompilation%and%DOTNET_TieredPGO%to controlTierandTierPGOrespectively