Re: [PATCH 1/5] Add a global synchronization point for pvclock

Jeremy Fitzhardinge
2010-04-23T19:22:35Z

On 04/23/2010 02:34 AM, Avi Kivity wrote:
>>
>> 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.

I presume the clobbers are needed for cpuid; if you use [lm]fence then
they shouldn't be needed, right?

J