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SubjectRe: Higher than expected disk write(2) latency
On Thu, 10 Jul 2008 15:17:47 +0200 Martin Sustrik <sustrik@fastmq.com> wrote:

> Hi Alan,
>
> >> What we see is that AIO performs rather bad while we are still
> >> enqueueing more writes (it misses right position on the disk and has to
> >> do superfluous disk revolvings), however, once we stop enqueueing new
> >> write request, those already in the queue are processed swiftly.
> >
> > Which disk scheduler are you using - some of the disk schedulers
> > intentionally delay writes to try and get better block merging.
>
> It's CFQ. Does it delay writes? And if so, what should we use instead?
>

noop is the simplest scheduler. deadline is the simplest real scheduler,
and deadline doesn't have any delaying logic.

If CFQ or anticipatory _are_ putting delays into this workload, that'd be
a bug.


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