Messages in this thread | | | Date | Sat, 24 Apr 2010 12:29:13 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 1/5] Add a global synchronization point for pvclock |
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On 04/24/2010 12:31 AM, Zachary Amsden wrote: > On 04/22/2010 11:34 PM, Avi Kivity wrote: >> On 04/23/2010 04:44 AM, Zachary Amsden wrote: >>> Or apply this patch. >>> time-warp.patch >>> >>> >>> diff -rup a/time-warp-test.c b/time-warp-test.c >>> --- a/time-warp-test.c 2010-04-15 16:30:13.955981607 -1000 >>> +++ b/time-warp-test.c 2010-04-15 16:35:37.777982377 -1000 >>> @@ -91,7 +91,7 @@ static inline unsigned long long __rdtsc >>> { >>> DECLARE_ARGS(val, low, high); >>> >>> - asm volatile("cpuid; rdtsc" : EAX_EDX_RET(val, low, high)); >>> + asm volatile("cpuid; rdtsc" : EAX_EDX_RET(val, low, high) :: >>> "ebx", "ecx"); >>> >> >> Plus, replace cpuid by lfence/mfence. cpuid will trap. >> > > Does lfence / mfence actually serialize? I thought there was some > great confusion about that not being the case on all AMD processors, > and possibly not at all on Intel.
They don't.
> > A trap, however is a great way to serialize. > > I think, there is no serializing instruction which can be used from > userspace which does not trap, at least, I don't know one off the top > of my head.
iret.
-- Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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