Hi Paolo, On Tue, Oct 21, 2014 at 08:39:49PM +0200, Paolo Bonzini wrote: > > >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. >
As you know, kernel build which Feng used is a CPU bound workload, so why 22.28% samples is halt? Regards, Wanpeng Li >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. > >Paolo >-- >To unsubscribe from this list: send the line "unsubscribe kvm" in >the body of a message to [email protected] >More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
