From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756576Ab2JDMoY (ORCPT ); Thu, 4 Oct 2012 08:44:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:13938 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756200Ab2JDMoX (ORCPT ); Thu, 4 Oct 2012 08:44:23 -0400 Message-ID: <506D8497.1040105@redhat.com> Date: Thu, 04 Oct 2012 14:44:07 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 MIME-Version: 1.0 To: Raghavendra K T CC: Peter Zijlstra , "H. Peter Anvin" , Marcelo Tosatti , Ingo Molnar , Rik van Riel , Srikar , "Nikunj A. Dadhania" , KVM , Jiannan Ouyang , chegu vinod , "Andrew M. Theurer" , LKML , Srivatsa Vaddagiri , Gleb Natapov , Andrew Jones Subject: Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios in PLE handler References: <1348486479.11847.46.camel@twins> <50604988.2030506@linux.vnet.ibm.com> <1348490165.11847.58.camel@twins> <50606050.309@linux.vnet.ibm.com> <1348494895.11847.64.camel@twins> <50606B33.1040102@linux.vnet.ibm.com> <5061B437.8070300@linux.vnet.ibm.com> <5064101A.5070902@redhat.com> <50643745.6010202@linux.vnet.ibm.com> <506440AF.9080202@redhat.com> <20121003142942.GB15253@linux.vnet.ibm.com> <506C7524.2010103@redhat.com> <506D6B64.6030907@linux.vnet.ibm.com> In-Reply-To: <506D6B64.6030907@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/04/2012 12:56 PM, Raghavendra K T wrote: > On 10/03/2012 10:55 PM, Avi Kivity wrote: >> On 10/03/2012 04:29 PM, Raghavendra K T wrote: >>> * Avi Kivity [2012-09-27 14:03:59]: >>> >>>> On 09/27/2012 01:23 PM, Raghavendra K T wrote: >>>>>> >>> [...] >>>>> 2) looking at the result (comparing A & C) , I do feel we have >>>>> significant in iterating over vcpus (when compared to even vmexit) >>>>> so We still would need undercommit fix sugested by PeterZ >>>>> (improving by >>>>> 140%). ? >>>> >>>> Looking only at the current runqueue? My worry is that it misses a lot >>>> of cases. Maybe try the current runqueue first and then others. >>>> >>> >>> Okay. Do you mean we can have something like >>> >>> + if (rq->nr_running == 1 && p_rq->nr_running == 1) { >>> + yielded = -ESRCH; >>> + goto out_irq; >>> + } >>> >>> in the Peter's patch ? >>> >>> ( I thought lot about && or || . Both seem to have their own cons ). >>> But that should be only when we have short term imbalance, as PeterZ >>> told. >> >> I'm missing the context. What is p_rq? > > p_rq is the run queue of target vcpu. > What I was trying below was to address Rik concern. Suppose > rq of source vcpu has one task, but target probably has two task, > with a eligible vcpu waiting to be scheduled. > >> >> What I mean was: >> >> if can_yield_to_process_in_current_rq >> do that >> else if can_yield_to_process_in_other_rq >> do that >> else >> return -ESRCH > > I think you are saying we have to check the run queue of the > source vcpu, if we have a vcpu belonging to same VM and try yield to > that? ignoring whatever the target vcpu we received for yield_to. > > Or is it that kvm_vcpu_yield_to should now check the vcpus of same vm > belonging to same run queue first. If we don't succeed, go again for > a vcpu in different runqueue. Right. Prioritize vcpus that are cheap to yield to. But may return bad results if all vcpus on the current runqueue are spinners, so probably not a good idea. > Does it add more overhead especially in <= 1x scenario? The current runqueue should have just our vcpu in that case, so low overhead. But it's a bad idea due to the above scenario. -- error compiling committee.c: too many arguments to function