Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752337AbdHBQrJ (ORCPT ); Wed, 2 Aug 2017 12:47:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58068 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752091AbdHBQq4 (ORCPT ); Wed, 2 Aug 2017 12:46:56 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 5773213A42 Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=pbonzini@redhat.com Subject: Re: [stable 4.4: PATCH] sched/cputime: Fix prev steal time accouting during CPU hotplug To: Andres Oportus , stable@vger.kernel.org Cc: LKML , Wanpeng Li , "Peter Zijlstra (Intel)" , Frederic Weisbecker , Linus Torvalds , Mike Galbraith , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Rik van Riel , Thomas Gleixner , Ingo Molnar , Greg Kroah-Hartman , Andres Oportus References: <1501561080-3459-1-git-send-email-andresoportus@android.com> From: Paolo Bonzini Message-ID: <4ff5a221-6564-db73-235b-cf638e8e9298@redhat.com> Date: Wed, 2 Aug 2017 18:46:46 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Wed, 02 Aug 2017 16:46:56 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3993 Lines: 103 On 02/08/2017 18:36, Andres Oportus wrote: > +Paolo Bonzini > > On Mon, Jul 31, 2017 at 9:18 PM, Andres Oportus > > wrote: > > commit 3d89e5478bf550a50c99e93adf659369798263b0 upstream. Not an easy call because this is a guest patch that depends on a host patch. But since it is a corner case (CPU hotplug) and it was backported to 4.7 already, Acked-by: Paolo Bonzini Paolo > 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 time is smaller than > rq->prev_steal_time. > > However, this should never happen. Steal time 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 ("sched/cputime: Fix steal time accounting vs. > CPU hotplug"). > > Signed-off-by: Wanpeng Li > > Signed-off-by: Peter Zijlstra (Intel) > > Acked-by: Paolo Bonzini > > Cc: Frederic Weisbecker > > Cc: Linus Torvalds > > Cc: Mike Galbraith > > Cc: Peter Zijlstra > > Cc: Radim Krčmář > > Cc: Rik van Riel > > Cc: Thomas Gleixner > > Fixes: 'commit e9532e69b8d1 ("sched/cputime: Fix steal time > accounting vs. CPU hotplug")' > Link: > http://lkml.kernel.org/r/1465813966-3116-3-git-send-email-wanpeng.li@hotmail.com > > Signed-off-by: Ingo Molnar > > Signed-off-by: Greg Kroah-Hartman > > Signed-off-by: Andres Oportus > > --- > 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 c436426..b103b9c 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5553,7 +5553,6 @@ migration_call(struct notifier_block *nfb, > unsigned long action, void *hcpu) > > case CPU_UP_PREPARE: > rq->calc_load_update = calc_load_update; > - account_reset_rq(rq); > break; > > case CPU_ONLINE: > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 4e5db65..55d92a1 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1770,16 +1770,3 @@ static inline u64 irq_time_read(int cpu) > } > #endif /* CONFIG_64BIT */ > #endif /* CONFIG_IRQ_TIME_ACCOUNTING */ > - > -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 > -} > -- > 1.9.1 > >