Messages in this thread | | | Subject | Re: [stable 4.4: PATCH] sched/cputime: Fix prev steal time accouting during CPU hotplug | From | Paolo Bonzini <> | Date | Wed, 2 Aug 2017 18:46:46 +0200 |
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On 02/08/2017 18:36, Andres Oportus wrote: > +Paolo Bonzini > > On Mon, Jul 31, 2017 at 9:18 PM, Andres Oportus > <andresoportus@android.com <mailto:andresoportus@android.com>> 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 <pbonzini@redhat.com>
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 <wanpeng.li@hotmail.com > <mailto:wanpeng.li@hotmail.com>> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org > <mailto:peterz@infradead.org>> > Acked-by: Paolo Bonzini <pbonzini@redhat.com > <mailto:pbonzini@redhat.com>> > Cc: Frederic Weisbecker <fweisbec@gmail.com <mailto:fweisbec@gmail.com>> > Cc: Linus Torvalds <torvalds@linux-foundation.org > <mailto:torvalds@linux-foundation.org>> > Cc: Mike Galbraith <efault@gmx.de <mailto:efault@gmx.de>> > Cc: Peter Zijlstra <peterz@infradead.org <mailto:peterz@infradead.org>> > Cc: Radim Krčmář <rkrcmar@redhat.com <mailto:rkrcmar@redhat.com>> > Cc: Rik van Riel <riel@redhat.com <mailto:riel@redhat.com>> > Cc: Thomas Gleixner <tglx@linutronix.de <mailto:tglx@linutronix.de>> > 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 > <http://lkml.kernel.org/r/1465813966-3116-3-git-send-email-wanpeng.li@hotmail.com> > Signed-off-by: Ingo Molnar <mingo@kernel.org <mailto:mingo@kernel.org>> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org > <mailto:gregkh@linuxfoundation.org>> > Signed-off-by: Andres Oportus <andresoportus@google.com > <mailto:andresoportus@google.com>> > --- > 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 > >
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