From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Ahern Subject: Re: [PATCH v2 00/11] KVM in-guest performance monitoring Date: Thu, 16 Jun 2011 11:16:09 -0600 Message-ID: <4DFA3A59.20007@cisco.com> References: <1307972106-2468-1-git-send-email-avi@redhat.com> <4DF66B1A.6060606@cisco.com> <4DF71DA3.2080300@redhat.com> <4DF7972F.3040103@cisco.com> <4DF79941.9050705@siemens.com> <4DF79B6F.10102@cisco.com> <4DF79EFE.1050201@cisco.com> <4DF7A436.8090308@cisco.com> <4DF873FD.6040903@redhat.com> <4DF8A82F.5090900@cisco.com> <4DF8B1F8.6030502@redhat.com> <4DF8D8FE.2080808@cisco.com> <4DF8DD87.8040905@redhat.com> <4DF8E328.6070708@cisco.com> <4DFA0AC4.9050702@redhat.com> <4DFA0E56.70301@cisco.com> <1308236915.13240.66.camel@twins> <4DFA1F18.4090903@cisco.com> <1308238021.13240.84.camel@twins> <4DFA229A.1030004@cisco.com> <4DFA286A.1030006@redhat.com> <4DFA298B.9020206@cisco.com> <4DFA2FC8.4080704@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Peter Zijlstra , Marcelo Tosatti , kvm@vger.kernel.org, Ingo Molnar , Arnaldo Carvalho de Melo To: Avi Kivity Return-path: Received: from sj-iport-3.cisco.com ([171.71.176.72]:64037 "EHLO sj-iport-3.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753655Ab1FPRQL (ORCPT ); Thu, 16 Jun 2011 13:16:11 -0400 In-Reply-To: <4DFA2FC8.4080704@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 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