Re: Time sliced CFQ io scheduler

Nick Piggin
2004-12-08T00:55:09Z

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).

It also tends to degrade more gracefully under memory load because
it doesn't require much readahead.

> 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.