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

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Date:	Fri, 4 Dec 2009 16:21:20 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH]cfq-iosched: make nonrot check logic consistent

On Thu, Dec 03, 2009 at 08:00:21PM +0800, Jens Axboe wrote:
> 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.
-next has the same issue too. Below is updated patch.

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>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 08b057b..abc5206 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1795,7 +1795,8 @@ static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 		return false;
 
 	/* We do for queues that were marked with idle window flag. */
-	if (cfq_cfqq_idle_window(cfqq))
+	if (cfq_cfqq_idle_window(cfqq) &&
+	   !(blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag))
 		return true;
 
 	/*
--
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