Re: [PATCH] Allow ACPI state change with active cpupools

[Juergen Gross <juergen.gross@ts.fujitsu.com>]

On 03/20/2012 03:55 PM, Keir Fraser wrote:
> On 20/03/2012 14:46, "Juergen Gross"<juergen.gross@ts.fujitsu.com>  wrote:
>
>>> Is it better to have cpupools know about offlining/suspend, or have
>>> offlining/suspend know about cpupools? I would have thought the latter makes
>>> more sense since it is offlining/suspend which calls into the cpupool
>>> subsystem.
>> I thought of a more relaxed solution in the cpupool coding:
>>
>> Instead of allowing to offline a cpu only if it is in Pool-0, I would allow it
>> if:
>> - the cpu is not the last one in the cpupool
>> - or no domain is active in the cpupool (this would include the suspend case,
>>     where all domains are paused)
>>
>> Together with your proposal to remember the cpupool for an offlined cpu to add
>> it again when it is onlined the handling should be rather simple and local.
> Ah, I see. Yes, a more flexible policy like this in the cpupool subsystem is
> best solution of all, imo.

I have a problem with that solution. I had to change cpu_disable_scheduler() to
do a vcpu_migrate() only if the vcpu is runnable. When the ACPI state change
isn't permanent like in poweroff case I don't want to change vcpu affinities.
This action might be necessary in vcpu_wake() if v->processor isn't usable for
the vcpu any more.

Unfortunately vcpu_migrate() is calling evtchn_move_pirqs(), which taking the
domain event channel lock. And vcpu_wake() is called at least by send_evtchn()
with that lock already hold...

Is it possible to use spin_lock_recursive() for the domain event channel lock?

Another solution would be to omit the vcpu_migrate() in cpu_disable_scheduler()
for paused vcpus only and to do it when unpausing the vcpu, but this would
leak scheduler internals...


Juergen

-- 
Juergen Gross                 Principal Developer Operating Systems
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