[Devel] Re: IO scheduler based IO controller V10

[Mike Galbraith]

On Fri, 2009-10-02 at 17:27 +0200, Corrado Zoccolo wrote:
> On Fri, Oct 2, 2009 at 2:49 PM, Vivek Goyal <vgoyal at redhat.com> wrote:
> > On Fri, Oct 02, 2009 at 12:55:25PM +0200, Corrado Zoccolo wrote:
> >
> > Actually I am not touching this code. Looking at the V10, I have not
> > changed anything here in idling code.
> 
> I based my analisys on the original patch:
> http://lkml.indiana.edu/hypermail/linux/kernel/0907.1/01793.html
> 
> Mike, can you confirm which version of the fairness patch did you use
> in your tests?

That would be this one-liner.

o CFQ provides fair access to disk in terms of disk time used to processes.
  Fairness is provided for the applications which have their think time with
  in slice_idle (8ms default) limit.

o CFQ currently disables idling for seeky processes. So even if a process
  has think time with-in slice_idle limits, it will still not get fair share
  of disk. Disabling idling for a seeky process seems good from throughput
  perspective but not necessarily from fairness perspecitve.

0 Do not disable idling based on seek pattern of process if a user has set
  /sys/block/<disk>/queue/iosched/fairness = 1.

Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
---
 block/cfq-iosched.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/block/cfq-iosched.c
===================================================================
--- linux-2.6.orig/block/cfq-iosched.c
+++ linux-2.6/block/cfq-iosched.c
@@ -1953,7 +1953,7 @@ cfq_update_idle_window(struct cfq_data *
 	enable_idle = old_idle = cfq_cfqq_idle_window(cfqq);
 
 	if (!atomic_read(&cic->ioc->nr_tasks) || !cfqd->cfq_slice_idle ||
-	    (cfqd->hw_tag && CIC_SEEKY(cic)))
+	    (!cfqd->cfq_fairness && cfqd->hw_tag && CIC_SEEKY(cic)))
 		enable_idle = 0;
 	else if (sample_valid(cic->ttime_samples)) {
 		if (cic->ttime_mean > cfqd->cfq_slice_idle)


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