Re: Time sliced CFQ io scheduler

Jens Axboe
2004-12-08T06:50:33Z

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