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SubjectRe: CFQ will be the new default IO scheduler - why?
Al Boldi wrote:
> Arjan van de Ven wrote:
>>>> Should there be a default scheduler per filesystem? As some
>>>> filesystems may perform better/worse with one over another?
>>> It's currently perDevice, and should probably be extended to perMount.
>> Hi,
>
> Hi!
>
>> per mount is going to be "not funny". I assume the situation you are
>> aiming for is the "3 partitions on a disk, each wants its own elevator".
>> The way the kernel currently works is that IO requests the filesystem
>> does are first flattened into an IO for the entire device (eg the
>> partition mapping is done) and THEN the IO scheduler gets involved to
>> schedule the IO on a per disk basis.
>
> IC. That probably explains why concurrent io-procs have such a hard time
> getting through to the disk. They probably just hang in the flatting phase,
> waiting for something to take care of their requests.
>
flattening is just an addition in the cpu, that's just really boring and shouldn't be visible anywhere
performance wise
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