linux-kernel - Re: [PATCH]cfq-iosched: make nonrot check logic consistent

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Date:	Thu, 3 Dec 2009 13:00:21 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH]cfq-iosched: make nonrot check logic consistent

On Thu, Dec 03 2009, Jens Axboe wrote:
> On Thu, Dec 03 2009, Shaohua Li wrote:
> > Send again, last post seems lost.
> > 
> > cfq_arm_slice_timer() has logic to disable idle window for SSD device. The same
> > thing should be done at cfq_select_queue() too, otherwise we will still see
> > idle window. This makes the nonrot check logic consistent in cfq.
> > Tests in a intel SSD with low_latency knob close, below patch can triple disk
> > thoughput for muti-thread sequential read.
> > 
> > Signed-off-by: Shaohua Li <shaohua.li@...el.com>
> > ---
> >  block/cfq-iosched.c |    3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > Index: linux/block/cfq-iosched.c
> > ===================================================================
> > --- linux.orig/block/cfq-iosched.c	2009-11-11 13:44:00.000000000 +0800
> > +++ linux/block/cfq-iosched.c	2009-11-11 13:45:33.000000000 +0800
> > @@ -1215,7 +1215,8 @@ static struct cfq_queue *cfq_select_queu
> >  	 * conditions to happen (or time out) before selecting a new queue.
> >  	 */
> >  	if (timer_pending(&cfqd->idle_slice_timer) ||
> > -	    (cfqq->dispatched && cfq_cfqq_idle_window(cfqq))) {
> > +	    (cfqq->dispatched && cfq_cfqq_idle_window(cfqq)
> > +	    && !(blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag))) {
> >  		cfqq = NULL;
> >  		goto keep_queue;
> >  	}
> 
> Thanks, applied to 2.6.33 queue.

On second check, we now hide that logic in cfq_should_idle() and as such
your patch no longer applies. I suggest you re-test with -next or my
for-2.6.33 branch, it has a big number of pending CFQ updates for
2.6.33.

-- 
Jens Axboe

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