Arjan van de Ven wrote: > 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 Try this on 2.6 and 2.4 respectively: # cat /dev/hda > /dev/null < switch to another vt > < login > < start timing > < wait for shell > < stop timing > < wait for dcache to be gobbled by cat and repeat login as necessary > On my system 2.4.31 (2sec) is at least twice as fast as 2.6.17 (4-10sec) depending on io-scheduler, with noop/deadline performing best, albeit a lot of noise (scrubbing the disk), and anti/cfq performing worst, albeit quieter (just hanging around). Thanks! -- Al - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
