From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755064Ab2JEJI7 (ORCPT ); Fri, 5 Oct 2012 05:08:59 -0400 Received: from e28smtp09.in.ibm.com ([122.248.162.9]:33268 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754990Ab2JEJIy (ORCPT ); Fri, 5 Oct 2012 05:08:54 -0400 Message-ID: <506EA2A4.8070309@linux.vnet.ibm.com> Date: Fri, 05 Oct 2012 14:34:36 +0530 From: Raghavendra K T Organization: IBM User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 MIME-Version: 1.0 To: Avi Kivity 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> <506D8497.1040105@redhat.com> In-Reply-To: <506D8497.1040105@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit x-cbid: 12100509-2674-0000-0000-00000639A4A3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/04/2012 06:14 PM, Avi Kivity wrote: > 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. Okay. 'll drop vcpu from same rq idea now. > >> 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. >