Re: [Ext2-devel] disk throughput

Jens Axboe
2001-11-05T07:19:26Z

On Sun, Nov 04 2001, Mike Fedyk wrote:
> On Mon, Nov 05, 2001 at 08:06:35AM +0100, Jens Axboe wrote:
> > On Sun, Nov 04 2001, Andrew Morton wrote:
> > > The meaning of the parameter to elvtune is a complete mystery, and the
> > > code is uncommented crud (tautology). So I just used -r20000 -w20000.
> >
> > It's the number of sectors that are allowed to pass a request on the
> > queue, because of merges or inserts before that particular request. So
> > you want lower than that probably, and you want READ latency to be
> > smaller than WRITE latency too. The default I set is 8192/16384 iirc, so
> > go lower than this -- -r512 -w1024 or even lower just to check the
> > results.
> >
>
> Does the elevator do better with powers of two?

No, that doesn't matter.

> > > This was based on observing the request queue dynamics. We frequently
> > > fail to merge requests which really should be merged regardless of
> > > latency. Bumping the elvtune settings fixed it all. But once the
> > > fs starts writing data out contiguously it's all academic.
> >
> > Interesting, the 2.5 design prevents this since it doesn't account
> > merges as a penalty (like a seek). I can do something like that for 2.4
> > too, I'll do a patch for you to test.
> >
>
> I'd be very interested in this patch. Can you post it pubically?

Just posted :-)

--
Jens Axboe