[Devel] Re: IO scheduler based IO controller V10

[Vivek Goyal]

On Fri, Oct 02, 2009 at 05:32:00PM +0200, Mike Galbraith wrote:
> 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.
> 

Ok. Thanks. Sorry, I got confused and thought that you are using "io
controller patches" with fairness=1.

In that case, Corrado's suggestion of refining it further and disabling idling
for seeky process only on non-rotational media (SSD and hardware RAID), makes
sense to me.

Thanks
Vivek
  
> 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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