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[dm-devel] Re: IO scheduler based IO controller V10



On Fri, Oct 02 2009, Ray Lee wrote:
> On Fri, Oct 2, 2009 at 7:56 AM, Jens Axboe <jens axboe oracle com> wrote:
> > In some cases I wish we had a server vs desktop switch, since it would
> > decisions on this easier. I know you say that servers care about
> > latency, but not at all to the extent that desktops do. Most desktop
> > users would gladly give away the top of the performance for latency,
> > that's not true of most server users. Depends on what the server does,
> > of course.
> 
> If most of the I/O on a system exhibits seeky tendencies, couldn't the
> schedulers notice that and use that as the hint for what to optimize?
> 
> I mean, there's no switch better than the actual I/O behavior itself.

Heuristics like that have a tendency to fail. What's the cut-off point?
Additionally, heuristics based on past process/system behaviour also has
a tendency to be suboptimal, since things aren't static.

We already look at seekiness of individual processes or groups. IIRC,
as-iosched also keeps a per-queue tracking.

-- 
Jens Axboe


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