[all-commits] [llvm/llvm-project] 39ed3c: [clang-scan-deps] Fix contention when updating `Tr...
Alexandre Ganea via All-commits
all-commits at lists.llvm.org
Thu Apr 25 07:32:07 PDT 2024
Branch: refs/heads/main
Home: https://github.com/llvm/llvm-project
Commit: 39ed3c68e51f1b04fe2890db9006ae1b176b1582
https://github.com/llvm/llvm-project/commit/39ed3c68e51f1b04fe2890db9006ae1b176b1582
Author: Alexandre Ganea <37383324+aganea at users.noreply.github.com>
Date: 2024-04-25 (Thu, 25 Apr 2024)
Changed paths:
M clang/include/clang/Basic/FileManager.h
M clang/lib/Basic/FileManager.cpp
M clang/lib/Frontend/CompilerInstance.cpp
M clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp
Log Message:
-----------
[clang-scan-deps] Fix contention when updating `TrackingStatistic`s in hot code paths in `FileManager`. (#88427)
`FileManager::getDirectoryRef()` and `FileManager::getFileRef()` are hot code paths in `clang-scan-deps`. These functions are updating on every call a few atomics related to printing statistics, which causes contention on high core count machines.
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After this patch we make the variables local to the `FileManager`.
In our test case, this saves about 49 sec over 1 min 47 sec of `clang-scan-deps` run time (1 min 47 sec before, 58 sec after). These figures are after applying my suggestion in https://github.com/llvm/llvm-project/pull/88152#issuecomment-2049803229, that is:
```
static bool shouldCacheStatFailures(StringRef Filename) {
return true;
}
```
Without the above, there's just too much OS noise from the high volume of `status()` calls with regular non-modules C++ code. Tested on Windows with clang-cl.
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