Messages in this thread | | | Date | Fri, 23 Apr 2010 11:31:37 -1000 | From | Zachary Amsden <> | Subject | Re: [PATCH 1/5] Add a global synchronization point for pvclock |
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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.
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.
Zach
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