Re: [Xen-devel] [PATCH] x86/xen: resume timer irqs early

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 08/08/14 15:04, Boris Ostrovsky wrote:
> On 08/08/2014 06:41 AM, David Vrabel wrote:
>> On 07/08/14 18:29, Boris Ostrovsky wrote:
>>> On 08/07/2014 01:16 PM, David Vrabel wrote:
>>>> If the timer irqs are resumed during device resume it is possible in
>>>> certain circumstances for the resume to hang early on, before device
>>>> interrupts are resumed.
>>>>
>>>> It is not entirely clear what is occuring the point of the hang but I
>>>> think a task necessary for the resume calls schedule_timeout(),
>>>> waiting for a timer interrupt (which never arrives).  This failure may
>>>> require specific tasks to be running on the other VCPUs to trigger
>>>> (processes are not frozen during a suspend/resume if PREEMPT is
>>>> disabled).
>>>>
>>>> Add IRQF_EARLY_RESUME to the timer interrupts so they are resumed in
>>>> syscore_resume().
>>>>
>>>> Also add IRQF_NO_SUSPEND as it is not necessary to suspend the timer
>>>> interrupts and IRQF_FORCE_RESUME was already set.
>>>
>>> IRQF_NO_SUSPEND is a component of IRQF_TIMER.
>> So it is.  How about this instead?
> 
> The change makes sense so
> 
>     Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> 
> but I am curious whether you actually were able to prove that it in fact
> fixes the hang (the description doesn't make it clear).

Without the patch repeatedly migrating a VM would hang during resume
after < 500 iterations.  With the patch the VM was migrated > 8000 times
without a problem.

David


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