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