Re: [Xen-devel] Only CPU0 active after ACPI S3, xen 4.1.3

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.01.13 at 14:58, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> On 16/01/13 13:08, Jan Beulich wrote:
>>>>> On 16.01.13 at 12:58, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
>>> On 16/01/13 11:22, George Dunlap wrote:
>>>> Jan, the commit message isn't very informative -- can you point me to
>> Which commit message?
>>
>>>> a conversation describing the problem you're fixing wrt
>>>> suspend/resume, and/or describe what you were trying to do?  Given the
>>>> results, the whole thing about not disabling scheduling during suspend
>>>> seems a bit suspect...
>>> In particular, just on a fairly cursory bit of function call skimming,
>>> it looks like:
>>> * This change means that cpupool.c:cpu_callback() won't call
>>> cpupool_cpu_add() when resuming
>>> * cpupool_cpu_add() does a bunch of paperwork (which would be
>>> unnecessary given the changes re suspend), but also calls
>>> cpupool_assign_cpu_locked()
>>> * cpupool_assign_cpu_locked() calls schedule_cpu_switch()
>>> * schedule_cpu_switch() calls the scheduler's tick_resume()
>>>
>>> So is it possible that on resume ticks are not being re-enabled, or
>>> something like that?
>> I don't see a problem here - it's symmetric (nothing done on
>> suspend, and nothing done on resume).
> 
> Well it would be if it was only data, but it's not.  That's my point.  
> Before this changeset (xen-unstable 25079:d5ccb2d1dbd1), ticks were 
> suspended and resumed on the CPU (i.e., timer interrupts turned off and 
> on), and after the patch, they're not.  Doesn't suspend disable / muck 
> with timer interrupts?

Oh, I see. But assuming we don't want to re-introduce what
Juergen tried to fix back then, shouldn't we instead call
sched_tick_{suspend,resume}() directly? Wouldn't that even
be more consistent than relying on the calls hidden underneath
the CPU pool code?

Jan


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