[PATCH] D100348: [hwasan] Fix lock contention on thread creation.

[Evgenii Stepanov via Phabricator via llvm-commits]

eugenis created this revision.
eugenis added a reviewer: vitalybuka.
eugenis requested review of this revision.
Herald added a project: Sanitizers.
Herald added a subscriber: Sanitizers.

Do not hold the free/live thread list lock longer than necessary.
This change speeds up the following benchmark 10x.

constexpr int kTopThreads = 50;
constexpr int kChildThreads = 20;
constexpr int kChildIterations = 8;

void Thread() {

  for (int i = 0; i < kChildIterations; ++i) {
    std::vector<std::thread> threads;
    for (int i = 0; i < kChildThreads; ++i)
      threads.emplace_back([](){});
    for (auto& t : threads)
      t.join();
  }

}

int main() {

  std::vector<std::thread> threads;
  for (int i = 0; i < kTopThreads; ++i)
    threads.emplace_back(Thread);
  for (auto& t : threads)
    t.join();

}


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D100348

Files:
  compiler-rt/lib/hwasan/hwasan_thread_list.h


Index: compiler-rt/lib/hwasan/hwasan_thread_list.h
===================================================================
--- compiler-rt/lib/hwasan/hwasan_thread_list.h
+++ compiler-rt/lib/hwasan/hwasan_thread_list.h
@@ -86,17 +86,22 @@
   }
 
   Thread *CreateCurrentThread() {
-    Thread *t;
+    Thread *t = nullptr;
     {
       SpinMutexLock l(&list_mutex_);
       if (!free_list_.empty()) {
         t = free_list_.back();
         free_list_.pop_back();
-        uptr start = (uptr)t - ring_buffer_size_;
-        internal_memset((void *)start, 0, ring_buffer_size_ + sizeof(Thread));
-      } else {
-        t = AllocThread();
       }
+    }
+    if (t) {
+      uptr start = (uptr)t - ring_buffer_size_;
+      internal_memset((void *)start, 0, ring_buffer_size_ + sizeof(Thread));
+    } else {
+      t = AllocThread();
+    }
+    {
+      SpinMutexLock l(&list_mutex_);
       live_list_.push_back(t);
     }
     t->Init((uptr)t - ring_buffer_size_, ring_buffer_size_);
@@ -124,10 +129,12 @@
   void ReleaseThread(Thread *t) {
     RemoveThreadStats(t);
     t->Destroy();
-    SpinMutexLock l(&list_mutex_);
-    RemoveThreadFromLiveList(t);
-    free_list_.push_back(t);
     DontNeedThread(t);
+    {
+      SpinMutexLock l(&list_mutex_);
+      RemoveThreadFromLiveList(t);
+      free_list_.push_back(t);
+    }
   }
 
   Thread *GetThreadByBufferAddress(uptr p) {


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