Index: third_party/tcmalloc/chromium/src/base/spinlock_internal.cc |
diff --git a/third_party/tcmalloc/chromium/src/base/spinlock_internal.cc b/third_party/tcmalloc/chromium/src/base/spinlock_internal.cc |
index b5b6ca4074d5024ff11c782758da4ec9257c5c91..b9faddef2c6f09ea6ac234f2948bfd564ae3f425 100644 |
--- a/third_party/tcmalloc/chromium/src/base/spinlock_internal.cc |
+++ b/third_party/tcmalloc/chromium/src/base/spinlock_internal.cc |
@@ -42,6 +42,9 @@ |
#include "base/spinlock_internal.h" |
+// forward declaration for use by spinlock_*-inl.h |
+namespace base { namespace internal { static int SuggestedDelayNS(int loop); }} |
+ |
#if defined(_WIN32) |
#include "base/spinlock_win32-inl.h" |
#elif defined(__linux__) |
@@ -73,5 +76,27 @@ int32 SpinLockWait(volatile Atomic32 *w, int n, |
return v; |
} |
+// Return a suggested delay in nanoseconds for iteration number "loop" |
+static int SuggestedDelayNS(int loop) { |
+ // Weak pseudo-random number generator to get some spread between threads |
+ // when many are spinning. |
+ static base::subtle::Atomic64 rand; |
+ uint64 r = base::subtle::NoBarrier_Load(&rand); |
+ r = 0x5deece66dLL * r + 0xb; // numbers from nrand48() |
+ base::subtle::NoBarrier_Store(&rand, r); |
+ |
+ r <<= 16; // 48-bit random number now in top 48-bits. |
+ if (loop < 0 || loop > 32) { // limit loop to 0..32 |
+ loop = 32; |
+ } |
+ // loop>>3 cannot exceed 4 because loop cannot exceed 32. |
+ // Select top 20..24 bits of lower 48 bits, |
+ // giving approximately 0ms to 16ms. |
+ // Mean is exponential in loop for first 32 iterations, then 8ms. |
+ // The futex path multiplies this by 16, since we expect explicit wakeups |
+ // almost always on that path. |
+ return r >> (44 - (loop >> 3)); |
+} |
+ |
} // namespace internal |
} // namespace base |