Messages in this thread | | | Date | Fri, 20 Jan 2006 09:10:43 +0100 | From | Jens Axboe <> | Subject | Re: Fall back io scheduler for 2.6.15? |
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On Thu, Jan 19 2006, Nate Diller wrote: > On 1/16/06, Jens Axboe <axboe@suse.de> wrote: > > On Fri, Jan 13 2006, Andrew Morton wrote: > > > Mingming Cao <cmm@us.ibm.com> wrote: > > > > > > > > On 2.6.14, the > > > > fall back io scheduler (if the chosen io scheduler is not found) is set > > > > to the default io scheduler (anticipatory, in this case), but since > > > > 2.6.15-rc1, this semanistic is changed to fall back to noop. > > > > > > OK. And I assume that AS wasn't compiled, so that's why it fell back? > > > > > > I actually thought that elevator= got removed, now we have > > > /sys/block/sda/queue/scheduler. But I guess that's not very useful with > > > CONFIG_SYSFS=n. > > > > > > > Is there any reason to fall back to noop instead of as? It seems > > > > anticipatory is much better than noop for ext3 with large sequential > > > > write tests (i.e, 1G dd test) ... > > > > > > I suspect that was an accident. Jens? > > > > It is, it makes more sense to fallback to the default of course. > > Not an accident at all, actually, because the original patch i > submitted allowed you to select a scheduler as 'default' even if it > were compiled as a module in kconfig. Since noop is guaranteed to be > present in any system, it is the obvious choice if the chosen or > default scheduler is not loaded.
Yes and that was a bug in that patch. The default scheduler must be builtin, that's a given. The Kconfig rules should make a default selection as a module illegal. And they do, they have since been fixed.
> If you change it to fall back to the default, it will oops if the > default is not available.
It must be.
-- Jens Axboe
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