Re: [PATCH v2] sched/cputime: add steal clock warp handling

Rik van Riel
2016-06-03T13:10:22Z

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On Fri, 2016-06-03 at 13:21 +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> I observed that sometimes st is 100% instantaneous, then idle is
> 100%
> even if there is a cpu hog on the guest cpu after the cpu hotplug
> comes
> back(N.B. this can not always be readily reproduced). I add trace to
> capture it as below:
>
> cpuhp/1-12    [001] d.h1   167.461657: account_process_tick: steal =
> 1291385514, prev_steal_time = 0
> cpuhp/1-12    [001] d.h1   167.461659: account_process_tick:
> steal_jiffies = 1291
> <idle>-0     [001] d.h1   167.462663: account_process_tick: steal =
> 18732255, prev_steal_time = 1291000000
> <idle>-0     [001] d.h1   167.462664: account_process_tick:
> steal_jiffies = 18446744072437
>
> The steal clock warp and then steal_jiffies overflow.
>
> Rik also pointed out to me:
>
> >
> > I have seen stuff like that with live migration too, in the past
> This patch adds steal clock warp handling by a safe threshold to
> only
> apply steal times that are positive and smaller than one second (as
> long as nohz_full has the one second timer tick left), ignoring
> intervals
> that are negative or longer than a second, and using those to sync
> up
> the guest with the host.
>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>

Reviewed-by: Rik van Riel <riel@redhat.com>

--
All Rights Reversed.

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