On 06/16/2011 10:31 AM, Avi Kivity wrote:
> On 06/16/2011 07:04 PM, David Ahern wrote:
>>
>> On 06/16/2011 09:59 AM, Avi Kivity wrote:
>> > On 06/16/2011 06:34 PM, David Ahern wrote:
>> >> >
>> >> > main ()
>> >> > {
>> >> > int i;
>> >> >
>> >> > fork();
>> >> > fork();
>> >
>> > What happens without the two forks?
>> >
>>
>> you have a 1-billion instruction benchmark since there is only 1 process.
>>
>
> I mean in terms of the overhead. Is the overhead due to context
> switches being made more expensive by the pmu, or is it something else?
I figured you meant something else by the question.
>
> But there were only 337 context switches in your measurement, they
> couldn't possibly be so bad.
> Anyway I'll investigate it.
>
I don't think it's the context switching. See the email on perf-report
and perf-annotate from the host side while running perf-stat in the
guest. Perhaps more vmexits and associated preemption disable/enable
overhead - or the rcu change?
David
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