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runtime: fix cputicks on x86

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See the following issue for context:
https://github.com/golang/go/issues/9729#issuecomment-74648287
In short, RDTSC can produce skewed results without preceding LFENCE/MFENCE.
Information on this matter is very scrappy in the internet.
But this is what linux kernel does (see rdtsc_barrier).
It also fixes the test program on my machine.

Update #9729

Change-Id: I3c1ffbf129fdfdd388bd5b7911b392b319248e68
Reviewed-on: https://go-review.googlesource.com/5033
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Dmitry Vyukov 2015-02-17 14:25:49 +03:00
parent 5868ce3519
commit 6e70fddec0
4 changed files with 50 additions and 12 deletions
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8
src/runtime/runtime2.go
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@ -562,12 +562,16 @@ var (
goos *int8
ncpu int32
iscgo bool
cpuid_ecx uint32
cpuid_edx uint32
signote note
forcegc forcegcstate
sched schedt
newprocs int32
// Information about what cpu features are available.
// Set on startup in asm_{x86,amd64}.s.
cpuid_ecx uint32
cpuid_edx uint32
lfenceBeforeRdtsc bool
)
/*