From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965454AbcFMKoU (ORCPT ); Mon, 13 Jun 2016 06:44:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57753 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965140AbcFMKoT (ORCPT ); Mon, 13 Jun 2016 06:44:19 -0400 Subject: Re: [PATCH v6 2/3] sched/cputime: Fix prev steal time accouting during cpu hotplug To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1465813966-3116-1-git-send-email-wanpeng.li@hotmail.com> <1465813966-3116-3-git-send-email-wanpeng.li@hotmail.com> Cc: Wanpeng Li , Ingo Molnar , "Peter Zijlstra (Intel)" , Rik van Riel , Thomas Gleixner , Frederic Weisbecker , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= From: Paolo Bonzini Message-ID: Date: Mon, 13 Jun 2016 12:44:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.0 MIME-Version: 1.0 In-Reply-To: <1465813966-3116-3-git-send-email-wanpeng.li@hotmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Mon, 13 Jun 2016 10:44:18 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13/06/2016 12:32, Wanpeng Li wrote: > From: Wanpeng Li > > Commit e9532e69b8d1 ("sched/cputime: Fix steal time accounting vs. CPU > hotplug") set rq->prev_* to 0 after a cpu hotplug comes back in order to > fix the case where (after CPU hotplug) steal is smaller than > rq->prev_steal_time. > > However, this should never happen. steal was only smaller because of the > KVM-specific bug fixed by the previous patch. Worse, the previous patch > triggers a bug on CPU hot-unplug/plug operation: because > rq->prev_steal_time is cleared, all of the CPU's past steal time will be > accounted again on hot-plug. > > Since the root cause has been fixed, we can just revert commit e9532e69b8d1. > > Fixes: 'commit e9532e69b8d1 ("sched/cputime: Fix steal time accounting vs. CPU hotplug")' > Cc: Ingo Molnar > Cc: Peter Zijlstra (Intel) > Cc: Rik van Riel > Cc: Thomas Gleixner > Cc: Frederic Weisbecker > Cc: Paolo Bonzini > Cc: Radim Krčmář > Signed-off-by: Wanpeng Li > --- > kernel/sched/core.c | 1 - > kernel/sched/sched.h | 13 ------------- > 2 files changed, 14 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 7f2cae4..7d45bb3 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -7213,7 +7213,6 @@ static void sched_rq_cpu_starting(unsigned int cpu) > struct rq *rq = cpu_rq(cpu); > > rq->calc_load_update = calc_load_update; > - account_reset_rq(rq); > update_max_interval(); > } > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 72f1f30..de607e4 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1809,16 +1809,3 @@ static inline void cpufreq_trigger_update(u64 time) {} > #else /* arch_scale_freq_capacity */ > #define arch_scale_freq_invariant() (false) > #endif > - > -static inline void account_reset_rq(struct rq *rq) > -{ > -#ifdef CONFIG_IRQ_TIME_ACCOUNTING > - rq->prev_irq_time = 0; > -#endif > -#ifdef CONFIG_PARAVIRT > - rq->prev_steal_time = 0; > -#endif > -#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING > - rq->prev_steal_time_rq = 0; > -#endif > -} > Acked-by: Paolo Bonzini