Re: [Xen-users] io scheduler

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> Cool. I didn't know some of this stuff existed...  e.g.
> Documentation/block/ioprio.txt

Yeah, it's pretty funky stuff :-)

> Can anyone tell what (if any) knowledge XEN has of this? Can it pass I/O
> priorities from a domU to the dom0, or can we assign I/O priorities to a
> whole domU ?

IIRC, there's some work going on to allow the second of those points, think 
there's a patch circulating.

Re. passing priorities through...  you get to do that implicitly, by the order 
in which domU requests come through.  But this obviously doesn't give a 
priority relative to domUs...  You could implement something like that but 
you'd have to trust all your domUs not to starve each other and dom0 itself, 
so it'd probably not be so widely applicable.

Definitely handy that this stuff is in the kernel though - IIRC, the pluggable 
scheduler stuff went in last year, so it's quite recent.

Cheers,
Mark


>
> On Mon, 9 Jan 2006, Mogens Valentin wrote:
>
> <snip>
>
> > On non-xen, yes. There's some benchmarks somewhere (don't seem to find
> > them right now) about advanteges of the various ones.
> > /usr/src/linux/Documentation/kernel-parameters.txt  says a few words.
> >
> > As you've seen for yourself, the scheduler can be changed runtime, and
> > likewise as a boot option.
> > My understanding is that schedulers works fairly directly on hardware,
> > at least reorganizing disk queues, I -think- you cannot have different
> > schedulers for dom0 and domU's.
> > Why would you? It's the same physical disk...
> > I believe cfq is usually considered the most versatile, unless specific
> > needs are determined.
>
> Looks that way...  from my 5 minutes of reading...
>
> -Tom
>
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