6ed2b425af
- spinlock-rand.patch fixes an issue encountered on PPC with undefined conversions from 'base::subtle::Atomic64*' to 'const volatile Atomic32*' OBS-URL: https://build.opensuse.org/request/show/146470 OBS-URL: https://build.opensuse.org/package/show/devel:libraries:c_c++/gperftools?expand=0&rev=13
38 lines
1.5 KiB
Diff
38 lines
1.5 KiB
Diff
diff --git a/src/base/spinlock_internal.cc b/src/base/spinlock_internal.cc
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index b9fadde..172a637 100644
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--- a/src/base/spinlock_internal.cc
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+++ b/src/base/spinlock_internal.cc
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@@ -80,6 +80,7 @@ int32 SpinLockWait(volatile Atomic32 *w, int n,
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static int SuggestedDelayNS(int loop) {
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// Weak pseudo-random number generator to get some spread between threads
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// when many are spinning.
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+#ifdef BASE_HAS_ATOMIC64
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static base::subtle::Atomic64 rand;
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uint64 r = base::subtle::NoBarrier_Load(&rand);
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r = 0x5deece66dLL * r + 0xb; // numbers from nrand48()
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@@ -96,6 +97,24 @@ static int SuggestedDelayNS(int loop) {
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// The futex path multiplies this by 16, since we expect explicit wakeups
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// almost always on that path.
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return r >> (44 - (loop >> 3));
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+#else
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+ static Atomic32 rand;
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+ uint32 r = base::subtle::NoBarrier_Load(&rand);
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+ r = 0x343fd * r + 0x269ec3; // numbers from MSVC++
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+ base::subtle::NoBarrier_Store(&rand, r);
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+
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+ r <<= 1; // 31-bit random number now in top 31-bits.
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+ if (loop < 0 || loop > 32) { // limit loop to 0..32
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+ loop = 32;
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+ }
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+ // loop>>3 cannot exceed 4 because loop cannot exceed 32.
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+ // Select top 20..24 bits of lower 31 bits,
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+ // giving approximately 0ms to 16ms.
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+ // Mean is exponential in loop for first 32 iterations, then 8ms.
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+ // The futex path multiplies this by 16, since we expect explicit wakeups
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+ // almost always on that path.
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+ return r >> (12 - (loop >> 3));
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+#endif
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}
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} // namespace internal
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