From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wanpeng Li Subject: Re: A question about HTL VM-Exit handling time Date: Tue, 28 Oct 2014 07:52:45 +0800 Message-ID: <20141027235245.GC27081@kernel> References: <5446A875.4080204@redhat.com> Reply-To: Wanpeng Li Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "kvm@vger.kernel.org" , Xiao Guangrong To: Paolo Bonzini Return-path: Received: from mga14.intel.com ([192.55.52.115]:26623 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752644AbaJ1ANj (ORCPT ); Mon, 27 Oct 2014 20:13:39 -0400 Content-Disposition: inline In-Reply-To: <5446A875.4080204@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 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 majordomo@vger.kernel.org >More majordomo info at http://vger.kernel.org/majordomo-info.html