[compiler-rt] 927efd0 - sanitizer_common: modernize SpinMutex

[Dmitry Vyukov via llvm-commits]

Author: Dmitry Vyukov
Date: 2021-07-21T08:14:12+02:00
New Revision: 927efd0b5d27985d7ac3e16f437b101f17df63de

URL: https://github.com/llvm/llvm-project/commit/927efd0b5d27985d7ac3e16f437b101f17df63de
DIFF: https://github.com/llvm/llvm-project/commit/927efd0b5d27985d7ac3e16f437b101f17df63de.diff

LOG: sanitizer_common: modernize SpinMutex

Some minor improvements:
1. Make StaticSpinMutex non-copyable.
2. Add LIKELY to Lock.
3. Move LockSlow into the .cpp file (now that we have it).
4. The only non-trivial change: use proc_yield(1) instread of proc_yield(10)
   with the proportional increase in the number of spin iterations.
   Latency of the PAUSE instruction has raised from ~1 cycle to ~100 cycles
   in the recent Intel CPUs. So proc_yield(10) is too aggressive backoff.

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D106350

Added: 
    

Modified: 
    compiler-rt/lib/sanitizer_common/sanitizer_mutex.cpp
    compiler-rt/lib/sanitizer_common/sanitizer_mutex.h

Removed: 
    


################################################################################
diff  --git a/compiler-rt/lib/sanitizer_common/sanitizer_mutex.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_mutex.cpp
index bc2d83c42c1a3..e2c17b239835d 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_mutex.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_mutex.cpp
@@ -16,6 +16,18 @@
 
 namespace __sanitizer {
 
+void StaticSpinMutex::LockSlow() {
+  for (int i = 0;; i++) {
+    if (i < 100)
+      proc_yield(1);
+    else
+      internal_sched_yield();
+    if (atomic_load(&state_, memory_order_relaxed) == 0 &&
+        atomic_exchange(&state_, 1, memory_order_acquire) == 0)
+      return;
+  }
+}
+
 void Semaphore::Wait() {
   u32 count = atomic_load(&state_, memory_order_relaxed);
   for (;;) {

diff  --git a/compiler-rt/lib/sanitizer_common/sanitizer_mutex.h b/compiler-rt/lib/sanitizer_common/sanitizer_mutex.h
index e3ff650b2c592..f146d4e17fe01 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_mutex.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_mutex.h
@@ -22,12 +22,14 @@ namespace __sanitizer {
 
 class MUTEX StaticSpinMutex {
  public:
+  StaticSpinMutex() = default;
+
   void Init() {
     atomic_store(&state_, 0, memory_order_relaxed);
   }
 
   void Lock() ACQUIRE() {
-    if (TryLock())
+    if (LIKELY(TryLock()))
       return;
     LockSlow();
   }
@@ -45,17 +47,10 @@ class MUTEX StaticSpinMutex {
  private:
   atomic_uint8_t state_;
 
-  void NOINLINE LockSlow() {
-    for (int i = 0;; i++) {
-      if (i < 10)
-        proc_yield(10);
-      else
-        internal_sched_yield();
-      if (atomic_load(&state_, memory_order_relaxed) == 0
-          && atomic_exchange(&state_, 1, memory_order_acquire) == 0)
-        return;
-    }
-  }
+  void LockSlow();
+
+  StaticSpinMutex(const StaticSpinMutex &) = delete;
+  void operator=(const StaticSpinMutex &) = delete;
 };
 
 class MUTEX SpinMutex : public StaticSpinMutex {
@@ -63,10 +58,6 @@ class MUTEX SpinMutex : public StaticSpinMutex {
   SpinMutex() {
     Init();
   }
-
- private:
-  SpinMutex(const SpinMutex &) = delete;
-  void operator=(const SpinMutex &) = delete;
 };
 
 // Semaphore provides an OS-dependent way to park/unpark threads.