Messages in this thread | | | Date | Wed, 8 Dec 2004 07:49:29 +0100 | From | Jens Axboe <> | Subject | Re: Time sliced CFQ io scheduler |
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On Wed, Dec 08 2004, Nick Piggin wrote: > On Wed, 2004-12-08 at 01:37 +0100, Andrea Arcangeli wrote: > > On Thu, Dec 02, 2004 at 08:52:36PM +0100, Jens Axboe wrote: > > > with its default io scheduler has basically zero write performance in > > > > IMHO the default io scheduler should be changed to cfq. as is all but > > general purpose so it's a mistake to leave it the default (plus as Jens > > I think it is actually pretty good at general purpose stuff. For > example, the old writes starve reads thing. It is especially bad > when doing small dependent reads like `find | xargs grep`. (Although > CFQ is probably better at this than deadline too).
Time sliced cfq fixes this.
> It also tends to degrade more gracefully under memory load because > it doesn't require much readahead.
Ditto.
> > found the write bandwidth is not existent during reads, no surprise it > > falls apart in any database load). We had to make the cfq the default > > for the enterprise release already. The first thing I do is to add > > elevator=cfq on a new install. I really like how well cfq has been > > designed, implemented and turned, Jens's results with his last patch are > > quite impressive. > > > > That is synch write bandwidth. Yes that seems to be a problem.
A pretty big one :-)
-- Jens Axboe
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