Messages in this thread | | | Subject | Re: [PATCH 4/8] Use prepare_to_wait_exclusive() instead prepare_to_wait() | From | Mike Galbraith <> | Date | Wed, 16 Dec 2009 06:43:44 +0100 |
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On Wed, 2009-12-16 at 09:48 +0900, KOSAKI Motohiro wrote: > > On 12/15/2009 12:32 AM, Mike Galbraith wrote: > > > On Tue, 2009-12-15 at 09:45 +0900, KOSAKI Motohiro wrote: > > >>> On 12/14/2009 07:30 AM, KOSAKI Motohiro wrote: > > >>>> if we don't use exclusive queue, wake_up() function wake _all_ waited > > >>>> task. This is simply cpu wasting. > > >>>> > > >>>> Signed-off-by: KOSAKI Motohiro<kosaki.motohiro@jp.fujitsu.com> > > >>> > > >>>> if (zone_watermark_ok(zone, sc->order, low_wmark_pages(zone), > > >>>> 0, 0)) { > > >>>> - wake_up(wq); > > >>>> + wake_up_all(wq); > > >>>> finish_wait(wq,&wait); > > >>>> sc->nr_reclaimed += sc->nr_to_reclaim; > > >>>> return -ERESTARTSYS; > > >>> > > >>> I believe we want to wake the processes up one at a time > > >>> here. > > > > >> Actually, wake_up() and wake_up_all() aren't different so much. > > >> Although we use wake_up(), the task wake up next task before > > >> try to alloate memory. then, it's similar to wake_up_all(). > > > > That is a good point. Maybe processes need to wait a little > > in this if() condition, before the wake_up(). That would give > > the previous process a chance to allocate memory and we can > > avoid waking up too many processes. > > if we really need wait a bit, Mike's wake_up_batch is best, I think. > It mean > - if another CPU is idle, wake up one process soon. iow, it don't > make meaningless idle.
Along those lines, there's also NEWIDLE balancing considerations. That idle may result in a task being pulled, which may or may not hurt a bit.
'course, if you're jamming up on memory allocation, that's the least of your worries, but every idle avoided is potentially a pull avoided.
Just a thought.
-Mike
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