Re: [PATCH 7/7] sched: implement try_to_wake_up_local()

[Tejun Heo <tj@kernel.org>]

Hello,

On 12/08/2009 05:53 PM, Peter Zijlstra wrote:
> On Mon, 2009-12-07 at 19:27 +0900, Tejun Heo wrote:
>>
>>> What happens when you run out of memory and the workqueue progress is
>>> needed to get free memory?
>>
>> That's when the "rescuer" workers kick in.  All workqueues which might
>> be used during allocation paths are required to have one.  When
>> manager fails to fork a new worker, it summons the rescuers.  They
>> migrate to the distressed cpu and processes only the works from their
>> specific workqueues thus guaranteeing forward progress.
> 
> What happens if the rescue worker is tied up on another cpu in a
> deadlock avoidance game, which requires progress on this cpu in order to
> resolve it?

Hmmm.... I think one rescuer thread per a workqueue is enough to
guarantee forward-progress.  If there are workqueues which have
inter-cpu dependency, we'll probably need per-cpu rescuers but is
there any?

Thanks.

-- 
tejun