[clang-tools-extra] 127a149 - [clangd] Add command-line flag to set background indexing thread priority.

[Sam McCall via cfe-commits]

Author: Sam McCall
Date: 2022-05-17T20:17:07+02:00
New Revision: 127a1492d72902e2b2cd8905c1198743761f52fb

URL: https://github.com/llvm/llvm-project/commit/127a1492d72902e2b2cd8905c1198743761f52fb
DIFF: https://github.com/llvm/llvm-project/commit/127a1492d72902e2b2cd8905c1198743761f52fb.diff

LOG: [clangd] Add command-line flag to set background indexing thread priority.

This is a followup to D124715, which changed the default, and it anticipates
future patches raising the priority of Low (which is currently equal to
Background on Windows & Linux).
The main point is to allow users to restore the old behavior, which e.g.
allows efficiency cores to remain idle.

I did consider making this a config setting, this is a more complicated change:
 - needs to touch queue priorities as well as thread priorities
 - we don't know the priority until evaluating the config inside the task
 - users would want the ability to prioritize background indexing tasks relative
   to each other without necessarily affecting thread priority, so using one
   option for both may be confusing
I don't really have a use case, so I prefer the simpler thing.

Differential Revision: https://reviews.llvm.org/D125673

Added: 
    

Modified: 
    clang-tools-extra/clangd/ClangdServer.h
    clang-tools-extra/clangd/index/Background.cpp
    clang-tools-extra/clangd/index/Background.h
    clang-tools-extra/clangd/tool/ClangdMain.cpp

Removed: 
    


################################################################################
diff  --git a/clang-tools-extra/clangd/ClangdServer.h b/clang-tools-extra/clangd/ClangdServer.h
index d1854c5f903ef..6d999722805ed 100644
--- a/clang-tools-extra/clangd/ClangdServer.h
+++ b/clang-tools-extra/clangd/ClangdServer.h
@@ -110,6 +110,7 @@ class ClangdServer {
     /// If true, ClangdServer automatically indexes files in the current project
     /// on background threads. The index is stored in the project root.
     bool BackgroundIndex = false;
+    llvm::ThreadPriority BackgroundIndexPriority = llvm::ThreadPriority::Low;
 
     /// If set, use this index to augment code completion results.
     SymbolIndex *StaticIndex = nullptr;

diff  --git a/clang-tools-extra/clangd/index/Background.cpp b/clang-tools-extra/clangd/index/Background.cpp
index 71860a3a4bcd2..b5349468eb24f 100644
--- a/clang-tools-extra/clangd/index/Background.cpp
+++ b/clang-tools-extra/clangd/index/Background.cpp
@@ -92,6 +92,7 @@ BackgroundIndex::BackgroundIndex(
     const ThreadsafeFS &TFS, const GlobalCompilationDatabase &CDB,
     BackgroundIndexStorage::Factory IndexStorageFactory, Options Opts)
     : SwapIndex(std::make_unique<MemIndex>()), TFS(TFS), CDB(CDB),
+      IndexingPriority(Opts.IndexingPriority),
       ContextProvider(std::move(Opts.ContextProvider)),
       IndexedSymbols(IndexContents::All),
       Rebuilder(this, &IndexedSymbols, Opts.ThreadPoolSize),
@@ -165,6 +166,7 @@ BackgroundQueue::Task BackgroundIndex::indexFileTask(std::string Path) {
       elog("Indexing {0} failed: {1}", Path, std::move(Error));
   });
   T.QueuePri = IndexFile;
+  T.ThreadPri = IndexingPriority;
   T.Tag = std::move(Tag);
   T.Key = Key;
   return T;

diff  --git a/clang-tools-extra/clangd/index/Background.h b/clang-tools-extra/clangd/index/Background.h
index 97f9095ed2c23..688c09814cd25 100644
--- a/clang-tools-extra/clangd/index/Background.h
+++ b/clang-tools-extra/clangd/index/Background.h
@@ -136,6 +136,8 @@ class BackgroundIndex : public SwapIndex {
     // Arbitrary value to ensure some concurrency in tests.
     // In production an explicit value is specified.
     size_t ThreadPoolSize = 4;
+    // Thread priority when indexing files.
+    llvm::ThreadPriority IndexingPriority = llvm::ThreadPriority::Low;
     // Callback that provides notifications as indexing makes progress.
     std::function<void(BackgroundQueue::Stats)> OnProgress = nullptr;
     // Function called to obtain the Context to use while indexing the specified
@@ -194,6 +196,7 @@ class BackgroundIndex : public SwapIndex {
   // configuration
   const ThreadsafeFS &TFS;
   const GlobalCompilationDatabase &CDB;
+  llvm::ThreadPriority IndexingPriority;
   std::function<Context(PathRef)> ContextProvider;
 
   llvm::Error index(tooling::CompileCommand);

diff  --git a/clang-tools-extra/clangd/tool/ClangdMain.cpp b/clang-tools-extra/clangd/tool/ClangdMain.cpp
index d86b5dab51e99..76cfaf7a35dfe 100644
--- a/clang-tools-extra/clangd/tool/ClangdMain.cpp
+++ b/clang-tools-extra/clangd/tool/ClangdMain.cpp
@@ -169,6 +169,21 @@ opt<bool> EnableBackgroundIndex{
     init(true),
 };
 
+opt<llvm::ThreadPriority> BackgroundIndexPriority{
+    "background-index-priority",
+    cat(Features),
+    desc("Thread priority for building the background index. "
+         "The effect of this flag is OS-specific."),
+    values(clEnumValN(llvm::ThreadPriority::Background, "background",
+                      "Minimum priority, runs on idle CPUs. "
+                      "May leave 'performance' cores unused."),
+           clEnumValN(llvm::ThreadPriority::Low, "low",
+                      "Reduced priority compared to interactive work."),
+           clEnumValN(llvm::ThreadPriority::Default, "normal",
+                      "Same priority as other clangd work.")),
+    init(llvm::ThreadPriority::Low),
+};
+
 opt<bool> EnableClangTidy{
     "clang-tidy",
     cat(Features),
@@ -876,6 +891,7 @@ clangd accepts flags on the commandline, and in the CLANGD_FLAGS environment var
   }
 #endif
   Opts.BackgroundIndex = EnableBackgroundIndex;
+  Opts.BackgroundIndexPriority = BackgroundIndexPriority;
   Opts.ReferencesLimit = ReferencesLimit;
   auto PAI = createProjectAwareIndex(loadExternalIndex, Sync);
   if (StaticIdx) {