TCMalloc: reduce waiting time in SpinLockDelay on Linux

Because of an optimization in Unlock(), we can't expect explicit
wake-ups and shouldn't wait for too long in SpinLockDelay.

BUG=168139
NOTRY=true


Review URL: https://chromiumcodereview.appspot.com/11784009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175543 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 5 insertions, 5 deletions

diff --git a/third_party/tcmalloc/chromium/src/base/spinlock_linux-inl.h b/third_party/tcmalloc/chromium/src/base/spinlock_linux-inl.h
index c190d52..4a1498d 100644
--- a/third_party/tcmalloc/chromium/src/base/spinlock_linux-inl.h
+++ b/third_party/tcmalloc/chromium/src/base/spinlock_linux-inl.h
@@ -87,16 +87,16 @@ void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop) {
     struct timespec tm;
     tm.tv_sec = 0;
     if (have_futex) {
+      // Wait between 0-16ms.
       tm.tv_nsec = base::internal::SuggestedDelayNS(loop);
-    } else {
-      tm.tv_nsec = 2000001;   // above 2ms so linux 2.4 doesn't spin
-    }
-    if (have_futex) {
-      tm.tv_nsec *= 16;  // increase the delay; we expect explicit wakeups
+      // Note: since Unlock() is optimized to not do a compare-and-swap,
+      // we can't expect explicit wake-ups. Therefore we shouldn't wait too
+      // long here.
       syscall(__NR_futex, reinterpret_cast<int *>(const_cast<Atomic32 *>(w)),
                 FUTEX_WAIT | futex_private_flag,
                 value, reinterpret_cast<struct kernel_timespec *>(&tm));
     } else {
+      tm.tv_nsec = 2000001;   // above 2ms so linux 2.4 doesn't spin
       nanosleep(&tm, NULL);
     }
     errno = save_errno;