From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH v6 2/3] sched/cputime: Fix prev steal time accouting during cpu hotplug Date: Mon, 13 Jun 2016 12:44:12 +0200 Message-ID: References: <1465813966-3116-1-git-send-email-wanpeng.li@hotmail.com> <1465813966-3116-3-git-send-email-wanpeng.li@hotmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Wanpeng Li , Ingo Molnar , "Peter Zijlstra (Intel)" , Rik van Riel , Thomas Gleixner , Frederic Weisbecker , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: In-Reply-To: <1465813966-3116-3-git-send-email-wanpeng.li@hotmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 13/06/2016 12:32, Wanpeng Li wrote: > From: Wanpeng Li >=20 > Commit e9532e69b8d1 ("sched/cputime: Fix steal time accounting vs. CP= U > 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. >=20 > However, this should never happen. steal was only smaller because of = the > KVM-specific bug fixed by the previous patch. Worse, the previous pa= tch > 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. >=20 > Since the root cause has been fixed, we can just revert commit e9532e= 69b8d1. >=20 > Fixes: 'commit e9532e69b8d1 ("sched/cputime: Fix steal time accountin= g 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 Kr=C4=8Dm=C3=A1=C5=99 > Signed-off-by: Wanpeng Li > --- > kernel/sched/core.c | 1 - > kernel/sched/sched.h | 13 ------------- > 2 files changed, 14 deletions(-) >=20 > 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 =3D cpu_rq(cpu); > =20 > rq->calc_load_update =3D calc_load_update; > - account_reset_rq(rq); > update_max_interval(); > } > =20 > 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 =3D 0; > -#endif > -#ifdef CONFIG_PARAVIRT > - rq->prev_steal_time =3D 0; > -#endif > -#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING > - rq->prev_steal_time_rq =3D 0; > -#endif > -} >=20 Acked-by: Paolo Bonzini