From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752621Ab2IUNxz (ORCPT ); Fri, 21 Sep 2012 09:53:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:11742 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750962Ab2IUNxx (ORCPT ); Fri, 21 Sep 2012 09:53:53 -0400 Message-ID: <505C712F.4060800@redhat.com> Date: Fri, 21 Sep 2012 09:52:47 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120827 Thunderbird/15.0 MIME-Version: 1.0 To: Takuya Yoshikawa CC: Raghavendra K T , Peter Zijlstra , "H. Peter Anvin" , Marcelo Tosatti , Ingo Molnar , Avi Kivity , Srikar , "Nikunj A. Dadhania" , KVM , Jiannan Ouyang , chegu vinod , "Andrew M. Theurer" , LKML , Srivatsa Vaddagiri , Gleb Natapov Subject: Re: [PATCH RFC 2/2] kvm: Be courteous to other VMs in overcommitted scenario in PLE handler References: <20120921115942.27611.67488.sendpatchset@codeblue> <20120921120019.27611.66093.sendpatchset@codeblue> <20120921224636.18cccbd6c33b161975f2a8cb@gmail.com> In-Reply-To: <20120921224636.18cccbd6c33b161975f2a8cb@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/21/2012 09:46 AM, Takuya Yoshikawa wrote: > On Fri, 21 Sep 2012 17:30:20 +0530 > Raghavendra K T wrote: > >> From: Raghavendra K T >> >> When PLE handler fails to find a better candidate to yield_to, it >> goes back and does spin again. This is acceptable when we do not >> have overcommit. >> But in overcommitted scenarios (especially when we have large >> number of small guests), it is better to yield. >> >> Reviewed-by: Srikar Dronamraju >> Signed-off-by: Raghavendra K T >> --- >> virt/kvm/kvm_main.c | 4 ++++ >> 1 files changed, 4 insertions(+), 0 deletions(-) >> >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> index 8323685..713b677 100644 >> --- a/virt/kvm/kvm_main.c >> +++ b/virt/kvm/kvm_main.c >> @@ -1660,6 +1660,10 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) >> } >> } >> } >> + /* In overcommitted cases, yield instead of spinning */ >> + if (!yielded && rq_nr_running() > 1) >> + schedule(); > > How about doing cond_resched() instead? Actually, an actual call to yield() may be better. That will set scheduler hints to make the scheduler pick another task for one round, while preserving this task's top position in the runqueue. -- All rights reversed