Re: CFQ will be the new default IO scheduler - why?

[Arjan van de Ven <arjan@linux.intel.com>]

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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