[PATCH] D57819: [clangd] Reduce number of threads used by BackgroundIndex to number of physical cores.

[Kadir Cetinkaya via Phabricator via cfe-commits]

kadircet created this revision.
kadircet added a reviewer: ilya-biryukov.
Herald added subscribers: cfe-commits, arphaman, jkorous, MaskRay, ioeric.
Herald added a project: clang.

clangd is using as many threads as logical cores for BackgroundIndex
by default. Due to hyper-threading this causes cache/branch-prediction misses
for AST and Preamble builts which slows them down.

This patch aims to change that default to number of physical cores to get rid of
that slow-down.


Repository:
  rCTE Clang Tools Extra

https://reviews.llvm.org/D57819

Files:
  clangd/index/Background.h


Index: clangd/index/Background.h
===================================================================
--- clangd/index/Background.h
+++ clangd/index/Background.h
@@ -67,11 +67,12 @@
   /// If BuildIndexPeriodMs is greater than 0, the symbol index will only be
   /// rebuilt periodically (one per \p BuildIndexPeriodMs); otherwise, index is
   /// rebuilt for each indexed file.
-  BackgroundIndex(Context BackgroundContext, const FileSystemProvider &,
-                  const GlobalCompilationDatabase &CDB,
-                  BackgroundIndexStorage::Factory IndexStorageFactory,
-                  size_t BuildIndexPeriodMs = 0,
-                  size_t ThreadPoolSize = llvm::hardware_concurrency());
+  BackgroundIndex(
+      Context BackgroundContext, const FileSystemProvider &,
+      const GlobalCompilationDatabase &CDB,
+      BackgroundIndexStorage::Factory IndexStorageFactory,
+      size_t BuildIndexPeriodMs = 0,
+      size_t ThreadPoolSize = llvm::heavyweight_hardware_concurrency());
   ~BackgroundIndex(); // Blocks while the current task finishes.
 
   // Enqueue translation units for indexing.


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