Re: [PATCH] sched/cputime: add steal clock warps handling during cpu hotplug

From	Wanpeng Li <kernellwp@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] sched/cputime: add steal clock warps handling during cpu hotplug
Date	2016-06-07 00:50 +0200
Message-ID	<rHbvj-2D4-3@gated-at.bofh.it> (permalink)
References	<rFzs5-5tU-3@gated-at.bofh.it> <rFzBM-5Mk-27@gated-at.bofh.it> <rFBtU-6Tw-15@gated-at.bofh.it> <rH34J-5B9-3@gated-at.bofh.it>
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2016-06-06 21:40 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> On 02/06/2016 15:59, Rik van Riel wrote:
>> If a guest is saved to disk and later restored (eg. after
>> a host reboot), or live migrated to another host, I would
>> expect to get totally disjoint steal time statistics from
>> the "new run" of the guest (which is the same run of the
>> guest OS).
>
> Why?  The preexisting guest steal time is always added to by
> KVM, so the time won't restart from zero.
>
> Continuing the previous count on CPU hot-unplug followed by hot-plug
> is less obvious, but I think it's overall the right thing to do.
>
> In fact, I was going to test a patch this week as simple as this:
>
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index eea2a6f72b31..1ef5e48b3a36 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -301,8 +301,6 @@ static void kvm_register_steal_time(void)
>         if (!has_steal_clock)
>                 return;
>
> -       memset(st, 0, sizeof(*st));
> -
>         wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED));
>         pr_info("kvm-stealtime: cpu %d, msr %llx\n",
>                 cpu, (unsigned long long) slow_virt_to_phys(st));

Thanks for the suggestion, I will try it today.

Regards,
Wanpeng Li

Thread

[PATCH] sched/cputime: add steal clock warps handling during cpu hotplug Wanpeng Li <kernellwp@gmail.com> - 2016-06-02 14:00 +0200
  Re: [PATCH] sched/cputime: add steal clock warps handling during cpu  hotplug Peter Zijlstra <peterz@infradead.org> - 2016-06-02 14:10 +0200
    Re: [PATCH] sched/cputime: add steal clock warps handling during  cpu hotplug Rik van Riel <riel@redhat.com> - 2016-06-02 16:10 +0200
      Re: [PATCH] sched/cputime: add steal clock warps handling during cpu hotplug Wanpeng Li <kernellwp@gmail.com> - 2016-06-03 07:40 +0200
      Re: [PATCH] sched/cputime: add steal clock warps handling during cpu  hotplug Paolo Bonzini <pbonzini@redhat.com> - 2016-06-06 15:50 +0200
        Re: [PATCH] sched/cputime: add steal clock warps handling during cpu hotplug Wanpeng Li <kernellwp@gmail.com> - 2016-06-07 00:50 +0200
        Re: [PATCH] sched/cputime: add steal clock warps handling during  cpu hotplug Rik van Riel <riel@redhat.com> - 2016-06-07 03:30 +0200
          Re: [PATCH] sched/cputime: add steal clock warps handling during cpu hotplug Wanpeng Li <kernellwp@gmail.com> - 2016-06-07 09:40 +0200
          Re: [PATCH] sched/cputime: add steal clock warps handling during cpu  hotplug Paolo Bonzini <pbonzini@redhat.com> - 2016-06-07 09:40 +0200

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