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[PATCH 1/5] cfq-iosched: Don't group_idle if cfqq has big thinktime

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  [PATCH 1/5] cfq-iosched: Don't group_idle if cfqq has big thinktime Jan Kara <jack@suse.cz> - 2016-01-07 16:30 +0100
    Re: [PATCH 1/5] cfq-iosched: Don't group_idle if cfqq has big  thinktime Tejun Heo <tj@kernel.org> - 2016-01-08 18:00 +0100
      Re: [PATCH 1/5] cfq-iosched: Don't group_idle if cfqq has big  thinktime Jan Kara <jack@suse.cz> - 2016-01-11 16:50 +0100

#1303661 — [PATCH 1/5] cfq-iosched: Don't group_idle if cfqq has big thinktime

From: Jan Kara <jack@suse.com>

There is no point in idling on a cfq group if the only cfq queue that is
there has too big thinktime.

Signed-off-by: Jan Kara <jack@suse.com>
---
 block/cfq-iosched.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 1f9093e901da..fcef1786edf3 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2897,6 +2897,7 @@ static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 static void cfq_arm_slice_timer(struct cfq_data *cfqd)
 {
 	struct cfq_queue *cfqq = cfqd->active_queue;
+	struct cfq_rb_root *st = cfqq->service_tree;
 	struct cfq_io_cq *cic;
 	unsigned long sl, group_idle = 0;
 
@@ -2947,8 +2948,13 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
 		return;
 	}
 
-	/* There are other queues in the group, don't do group idle */
-	if (group_idle && cfqq->cfqg->nr_cfqq > 1)
+	/*
+	 * There are other queues in the group or this is the only group and
+	 * it has too big thinktime, don't do group idle.
+	 */
+	if (group_idle &&
+	    (cfqq->cfqg->nr_cfqq > 1 ||
+	     !cfq_io_thinktime_big(cfqd, &st->ttime, true)))
 		return;
 
 	cfq_mark_cfqq_wait_request(cfqq);
-- 
2.6.2

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#1304735 — Re: [PATCH 1/5] cfq-iosched: Don't group_idle if cfqq has big thinktime

Hello, Jan.

On Thu, Jan 07, 2016 at 04:28:12PM +0100, Jan Kara wrote:
> @@ -2947,8 +2948,13 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
>  		return;
>  	}
>  
> -	/* There are other queues in the group, don't do group idle */
> -	if (group_idle && cfqq->cfqg->nr_cfqq > 1)
> +	/*
> +	 * There are other queues in the group or this is the only group and
> +	 * it has too big thinktime, don't do group idle.
> +	 */
> +	if (group_idle &&
> +	    (cfqq->cfqg->nr_cfqq > 1 ||
> +	     !cfq_io_thinktime_big(cfqd, &st->ttime, true)))
>  		return;

Is the negation in front of the cfq_io_thinktime_big() right?  That
doesn't seem to match the comment or description.  What am I missing?

Thanks.

-- 
tejun

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#1306428 — Re: [PATCH 1/5] cfq-iosched: Don't group_idle if cfqq has big thinktime

On Fri 08-01-16 11:58:31, Tejun Heo wrote:
> Hello, Jan.
> 
> On Thu, Jan 07, 2016 at 04:28:12PM +0100, Jan Kara wrote:
> > @@ -2947,8 +2948,13 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
> >  		return;
> >  	}
> >  
> > -	/* There are other queues in the group, don't do group idle */
> > -	if (group_idle && cfqq->cfqg->nr_cfqq > 1)
> > +	/*
> > +	 * There are other queues in the group or this is the only group and
> > +	 * it has too big thinktime, don't do group idle.
> > +	 */
> > +	if (group_idle &&
> > +	    (cfqq->cfqg->nr_cfqq > 1 ||
> > +	     !cfq_io_thinktime_big(cfqd, &st->ttime, true)))
> >  		return;
> 
> Is the negation in front of the cfq_io_thinktime_big() right?  That
> doesn't seem to match the comment or description.  What am I missing?

Ah, you are right! I wanted to make arming of group_idle timer consistent
with what we test in cfq_should_idle() for normal idle timer but I
accidentally reverted the condition. I'll fix this.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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