Re: Block I/O Schedulers: Can they be made selectable/device? @runtime?

[Valdis.Kletnieks@vt.edu]

On Sat, 25 Mar 2006 22:41:00 PST, Linda Walsh said:
> Is it still the case that block I/O schedulers (AS, CFQ, etc.)
> are only selectable at boot time?

Hasn't been for quite some time.  CPU schedulers are stuck at boot time, even
if you have the 'plugsched' patch (and if you don't, you're stuck with the one
scheduler in-tree currently).  There was a patch posted a few days ago
that allowed on-the-fly changing of plugsched, but that's still too bleeding
edge even for me... ;)

> How difficult would it be to allow multiple, concurrent I/O
> schedulers running on different block devices?

>From my /etc/rc.local:

echo cfq > /sys/block/hda/queue/scheduler
echo noop > /sys/block/hdb/queue/scheduler

(hda is a real disk with ext3 partitions on it, hdb is a DVD/CD/RW that almost
always has exactly one process reading or writing to it at a given time, so doing
things in the order requested is just fine).

Simple enough? ;)

(This *does* require that you built more than one scheduler, and possibly
to make sure they're loaded if you managed to build them modular...)

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