Re: Raw devices broken in 2.6.1? AND- 2.6.1 I/O degraded?

Andrew Morton
2004-01-30T06:45:52Z

"Curt" <curt@northarc.com> wrote:
>
> > Or you can put 2.6 on par by setting
> > /proc/sys/vm/dirty_background_ratio to 40 and dirty_ratio to 60.
>
> Okay will do, is there a good comprehensive resource where I can read up on
> these (and presumably many other I/O related) variables?

We've been relatively good about keeping the in-kernel documentation up to
date. For this stuff, see Documentation/filesystems/proc.txt and
Documentation/sysctl/vm.txt.

> > Longer-term, if your customers are using scsi, you should ensure that the
> > disks do not use a tag queue depth of more than 4 or 8. More than that
> and
> > the anticipatory scheduler becomes ineffective and you won't get that
> > multithreaded-read goodness.
>
> I've heard-tell of tweaking the elevator paramter to 'deadline', again could
> you point me to a resource where I can read up on this? And forgive the
> newbie-question, but is this a boot-time parameter, or a bit I can set in
> the /proc system, or both?

It's boot-time only. We were working on making it per-disk but that was
quite complex and we really didn't get there in time.

So add `elevator=deadline' to your kernel boot command line. From my
(brief) testing, it was a significant lose. It needs more work though:
2.6+deadline shouldn't be slower than 2.4.x

> > Please stay in touch, btw. If we cannot get applications such as yours
> > working well, we've wasted our time...
>
> I'll do what I can to provide real-world feedback, I want this to work too.

Thanks.