> -----Original Message-----
> From: Paolo Bonzini [mailto:paolo.bonz...@gmail.com] On Behalf Of Paolo
> Bonzini
> Sent: Wednesday, October 22, 2014 2:40 AM
> To: Wu, Feng; kvm@vger.kernel.org
> Cc: Xiao Guangrong
> Subject: Re: A question about HTL VM-Exit handling time
>
>
>
> On 10/16/2014 10:15 AM, Wu, Feng wrote:
> > Hi folks,
> >
> > I run kernel build in the guest and use perf kvm to get some VM-Exit result
> > as
> the following:
> >
> > Analyze events for all VCPUs:
> >
> > VM-EXIT Samples Samples% Time% Min Time
> Max Time A
> >
> > MSR_WRITE 3613908 57.53% 18.97%
> 5us 1362us 9.73
> > HLT 1399747 22.28% 74.90% 5us
> 432448us 99.24
> > CR_ACCESS 961203 15.30% 3.28%
> 4us 188us 6.33
> > EXTERNAL_INTERRUPT 213821 3.40% 2.25%
> 4us 4089us 19.54
> > EXCEPTION_NMI 25152 0.40% 0.12%
> 4us 71us 9.05
> > EPT_MISCONFIG 20104 0.32% 0.15%
> 8us 5628us 13.74
> > CPUID 19904 0.32% 0.07% 4us
> 220us 6.90
> > IO_INSTRUCTION 17097 0.27% 0.20% 13us
> 1008us 22.08
> > PAUSE_INSTRUCTION 10737 0.17% 0.05%
> 4us 53us 8.33
> > MSR_READ 48 0.00% 0.00%
> 4us 8us 5.62
> >
> > Total Samples:6281721, Total events handled time:185457820.41us.
> >
> > I also do some other experiments with different workload in the guest, I got
> the same results in terms of
> > HLT VM-Exit handling time. Does anyone know why the handling time for HLT
> VM-Exit is so high? Appreciate
> > You help!
>
> 432 ms sounds like a lot, but in general it is expected that HLT vmexits
> take a long time. After an HLT vmexit, the VCPU will not be reentered
> until the next interrupt comes. On hardware, the HLT instruction can
> also take many milliseconds.
Thanks for your answer, Paolo.
There is a general question for perf kvm. Do you know how the vmexit
handling time is measured? Such as what is the start point, and the
end point? If I got this information, I think I can better understand the
value of the handling time. Thanks a lot!
>
> If this is an SMP guest, it's possible that the maximum time is
> registered on the APs before Linux boots. With a UP guest I would
> expect a shorter maximum time, but still longer than other vmexits.
Yes, you are right, I get the data for an UP guest and the HLT vmexit
handling time is shorter. Here is the result:
Analyze events for all VCPUs:
VM-EXIT Samples Samples% Time% Min Time Max Time
EXTERNAL_INTERRUPT 90015 29.68% 41.92% 4us 660us
24.9
MSR_WRITE 89512 29.52% 14.25% 4us 162us
8.5
IO_INSTRUCTION 47823 15.77% 16.67% 11us 1907us
18.6
EPT_MISCONFIG 38504 12.70% 7.42% 7us 4848us
10.3
CPUID 32658 10.77% 3.61% 3us 304us
5.9
EXCEPTION_NMI 2232 0.74% 0.34% 4us 164us
8.2
PAUSE_INSTRUCTION 1594 0.53% 0.21% 3us 44us
6.9
HLT 547 0.18% 15.50% 8us 177098us
1516.5
CR_ACCESS 278 0.09% 0.05% 5us 26us
8.7
EPT_VIOLATION 71 0.02% 0.03% 8us 27us
20.3
MSR_READ 12 0.00% 0.00% 3us 4us
4.1
Total Samples:303246, Total events handled time:5350983.30us.
Thanks,
Feng
>
> Paolo
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