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SubjectRe: [RFC][PATCH v3 7/10] workqueue: add WQ_IDLEPRI
On Thu, 26 May 2011 13:44:06 +0200
Tejun Heo <tj@kernel.org> wrote:

> Hello,
>
> On Thu, May 26, 2011 at 07:50:19PM +0900, KAMEZAWA Hiroyuki wrote:
> > On Thu, 26 May 2011 19:30:18 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > > In the next version, I'll try some like..
> > > ==
> > > process_one_work(...) {
> > > .....
> > > spin_unlock_irq(&gcwq->lock);
> > > .....
> > > if (cwq->wq->flags & WQ_IDLEPRI) {
> > > set_scheduler(...SCHED_IDLE...)
> > > cond_resched();
> > > scheduler_switched = true;
> > > }
> > > f(work)
> > > if (scheduler_switched)
> > > set_scheduler(...SCHED_OTHER...)
> > > spin_lock_irq(&gcwq->lock);
> > > }
> > > ==
> > > Patch size will be much smaller. (Should I do this in memcg's code ??)
> > >
> >
> > BTW, my concern is that if f(work) is enough short,effect of SCHED_IDLE will never
> > be found because SCHED_OTHER -> SCHED_IDLE -> SCHED_OTHER switch is very fast.
> > Changed "weight" of CFQ never affects the next calculation of vruntime..of the
> > thread and the work will show the same behavior with SCHED_OTHER.
> >
> > I'm sorry if I misunderstand CFQ and setscheduler().
>
> Hmm... I'm not too familiar there either but,
>
> * If prio is lowered (you're gonna lower it too, right?),
> prio_changed_fair() is called which in turn does resched_task() as
> necessary.
>
> * More importantly, for short work items, it's likely to not matter at
> all. If you can determine beforehand that it's not gonna take very
> long time, queueing on system_wq would be more efficient.
>
> Thanks.
>

Ok, Now, I use following style.

(short work)->requeue->(short work)->requeue
I'll change this as
(set SCHED_IDLE)->long work (until the end)->(set SCHED_OTHER)

Then, I'll see what I want.

Thanks.
-Kame






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