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

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Date:	Fri, 23 Apr 2010 12:22:34 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Avi Kivity <avi@...hat.com>
CC:	Zachary Amsden <zamsden@...hat.com>,
	Glauber Costa <glommer@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock

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

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