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Re: [Xen-devel] [PATCH] xen: ensure timer tick is resumed even on CPU dr

To: Ian Campbell <ian.campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] xen: ensure timer tick is resumed even on CPU driving the resume
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Wed, 19 May 2010 11:02:19 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, stable@xxxxxxxxxx
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On 05/19/2010 08:36 AM, Ian Campbell wrote:
> The core suspend/resume code is run from stop_machine on CPU0 but
> parts of the suspend/resume machinery (including xen_arch_resume) are
> run on whichever CPU happened to schedule the xenwatch kernel thread.
> As part of the non-core resume code xen_arch_resume is called in order
> to restart the timer tick on non-boot processors. The boot processor
> itself is taken care of by core timekeeping code.
> xen_arch_resume uses smp_call_function which does not call the given
> function on the current processor. This means that we can end up with
> one CPU not receiving timer ticks if the xenwatch thread happened to
> be scheduled on CPU > 0.
> Use on_each_cpu instead of smp_call_function to ensure the timer tick
> is resumed everywhere.

Argh, that seems to be a pretty common trap to fall into.  Looks OK (but
unfortunately doesn't fix my other problem).

Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>


> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
> Cc: Stable Kernel <stable@xxxxxxxxxx>
> ---
>  arch/x86/xen/suspend.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
> index 987267f..a9c6611 100644
> --- a/arch/x86/xen/suspend.c
> +++ b/arch/x86/xen/suspend.c
> @@ -60,6 +60,6 @@ static void xen_vcpu_notify_restore(void *data)
>  void xen_arch_resume(void)
>  {
> -     smp_call_function(xen_vcpu_notify_restore,
> -                            (void *)CLOCK_EVT_NOTIFY_RESUME, 1);
> +     on_each_cpu(xen_vcpu_notify_restore,
> +                 (void *)CLOCK_EVT_NOTIFY_RESUME, 1);
>  }

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