> -----Original Message----- > From: Paolo Bonzini [mailto:paolo.bonzini@xxxxxxxxx] On Behalf Of Paolo > Bonzini > Sent: Wednesday, October 22, 2014 2:40 AM > To: Wu, Feng; kvm@xxxxxxxxxxxxxxx > 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 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
