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[dm-devel] Re: Regarding dm-ioband tests


Fabio Checconi <fchecconi gmail com> wrote:
> Hi,
> > From: Rik van Riel <riel redhat com>
> > Date: Tue, Sep 08, 2009 03:24:08PM -0400
> >
> > Ryo Tsuruta wrote:
> > >Rik van Riel <riel redhat com> wrote:
> > 
> > >>Are you saying that dm-ioband is purposely unfair,
> > >>until a certain load level is reached?
> > >
> > >Not unfair, dm-ioband(weight policy) is intentionally designed to
> > >use bandwidth efficiently, weight policy tries to give spare bandwidth
> > >of inactive groups to active groups.
> > 
> > This sounds good, except that the lack of anticipation
> > means that a group with just one task doing reads will
> > be considered "inactive" in-between reads.
> > 
>   anticipation helps in achieving fairness, but CFQ currently disables
> idling for nonrot+NCQ media, to avoid the resulting throughput loss on
> some SSDs.  Are we really sure that we want to introduce anticipation
> everywhere, not only to improve throughput on rotational media, but to
> achieve fairness too?

I'm also not sure if it's worth introducing anticipation everywhere.
The storage devices are becoming faster and smarter every year. In
practice, I did a benchmark with a SAN storage and the noop scheduler
got the best result.

However, I'll consider how IO from one task should take care of.

Ryo Tsuruta

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