[PATCH] Fall back io scheduler ( Re: [Ext2-devel] Re: Fall back io scheduler for 2.6.15?)

[Mingming Cao <cmm@us.ibm.com>]

On Mon, 2006-01-16 at 09:43 +0100, Jens Axboe 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.
> 

How about this one?


In the case the chosen io scheduler (elevator = "xxx") is not on the
registered list, fall back to default scheduler makes more sense.

Signed-off-by: Mingming Cao <cmm@us.ibm.com>


---

 linux-2.6.15-ming/block/elevator.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff -puN block/elevator.c~default-fall-back-scheduler-fix
block/elevator.c
--- linux-2.6.15/block/elevator.c~default-fall-back-scheduler-fix
2006-01-16 11:42:04.000446588 -0800
+++ linux-2.6.15-ming/block/elevator.c	2006-01-16 11:42:41.145131615
-0800
@@ -151,12 +151,12 @@ static void elevator_setup_default(void)
 		strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED);
 
  	/*
- 	 * If the given scheduler is not available, fall back to no-op.
+ 	 * If the given scheduler is not available, fall back to default.
  	 */
  	if ((e = elevator_find(chosen_elevator)))
 		elevator_put(e);
 	else
- 		strcpy(chosen_elevator, "noop");
+ 		strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED);
 }
 
 static int __init elevator_setup(char *str)

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