Re: Time sliced CFQ io scheduler

Jens Axboe
2004-12-08T07:29:58Z

On Wed, Dec 08 2004, Nick Piggin wrote:
> On Wed, 2004-12-08 at 08:11 +0100, Jens Axboe wrote:
> > On Wed, Dec 08 2004, Nick Piggin wrote:
> > > On Wed, 2004-12-08 at 07:55 +0100, Jens Axboe wrote:
>
> > > > Currently I think the time sliced cfq is the best all around. There's
> > > > still a few kinks to be shaken out, but generally I think the concept is
> > > > sounder than AS.
> > > >
> > >
> > > But aren't you basically unconditionally allowing a 4ms idle time after
> > > reads? The complexity of AS (other than all the work we had to do to get
> > > the block layer to cope with it), is getting it to turn off at (mostly)
> > > the right times. Other than that, it is basically the deadline
> > > scheduler.
> >
> > Yes, the concept is similar and there will be time wasting currently.
> > I've got some cases covered that AS doesn't, and there are definitely
> > some the other way around as well.
> >
>
> Oh? What have you got covered that AS doesn't? (I'm only reading the
> patch itself, which isn't trivial to follow).

You are only thinking in terms of single process characteristics like
will it exit and think times, the inter-process characteristics are very
hap hazard. You might find the applied code easier to read, I think.

> > If you have any test cases/programs, I'd like to see them.
> >
>
> Hmm, damn. Lots of stuff. I guess some of the notable ones that I've
> had trouble with are OraSim (Oracle might give you a copy), Andrew's
> patch scripts when applying a stack of patches, pgbench... can't
> really remember any others off the top of my head.

The patch scripts case is interesting, last night (when committing other
patches) I was thinking I should try and bench that today. It has a good
mix of reads and writes.

There's still lots of tuning in the pipe line. As I wrote originally,
this was basically just a quick hack that I was surprised did so well
:-) It has grown a little since then and I think the concept is really
sound, so I'll continue to work on it.

> I've got a small set of basic test programs that are similar to the
> sort of tests you've been running in this thread as well.

Ok

--
Jens Axboe