cfq-iosched: no need to keep track of busy_rt_queues

cfq-iosched: no need to keep track of busy_rt_queues

[Vivek Goyal]

o Get rid of busy_rt_queues infrastructure. Looks like it is redundant.

o Once an RT queue gets request it will preempt any of the BE or IDLE queues
  immediately. Otherwise this queue will be put on service tree and scheduler
  will anyway select this queue before any of the BE or IDLE queue. Hence
  looks like there is no need to keep track of how many busy RT queues are
  currently on service tree. 

o I ran one RT reader and two BE readers. Can't see preemption due to
  busy_rt_queues kicking in.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
 block/cfq-iosched.c |   24 ------------------------
 1 file changed, 24 deletions(-)

Index: linux5/block/cfq-iosched.c
===================================================================
--- linux5.orig/block/cfq-iosched.c	2009-07-09 16:30:46.000000000 -0400
+++ linux5/block/cfq-iosched.c	2009-07-09 16:31:48.000000000 -0400
@@ -134,11 +134,6 @@ struct cfq_data {
 	struct rb_root prio_trees[CFQ_PRIO_LISTS];
 
 	unsigned int busy_queues;
-	/*
-	 * Used to track any pending rt requests so we can pre-empt current
-	 * non-RT cfqq in service when this value is non-zero.
-	 */
-	unsigned int busy_rt_queues;
 
 	int rq_in_driver;
 	int sync_flight;
@@ -648,9 +643,6 @@ static void cfq_add_cfqq_rr(struct cfq_d
 	BUG_ON(cfq_cfqq_on_rr(cfqq));
 	cfq_mark_cfqq_on_rr(cfqq);
 	cfqd->busy_queues++;
-	if (cfq_class_rt(cfqq))
-		cfqd->busy_rt_queues++;
-
 	cfq_resort_rr_list(cfqd, cfqq);
 }
 
@@ -673,8 +665,6 @@ static void cfq_del_cfqq_rr(struct cfq_d
 
 	BUG_ON(!cfqd->busy_queues);
 	cfqd->busy_queues--;
-	if (cfq_class_rt(cfqq))
-		cfqd->busy_rt_queues--;
 }
 
 /*
@@ -1179,20 +1169,6 @@ static struct cfq_queue *cfq_select_queu
 		goto expire;
 
 	/*
-	 * If we have a RT cfqq waiting, then we pre-empt the current non-rt
-	 * cfqq.
-	 */
-	if (!cfq_class_rt(cfqq) && cfqd->busy_rt_queues) {
-		/*
-		 * We simulate this as cfqq timed out so that it gets to bank
-		 * the remaining of its time slice.
-		 */
-		cfq_log_cfqq(cfqd, cfqq, "preempt");
-		cfq_slice_expired(cfqd, 1);
-		goto new_queue;
-	}
-
-	/*
 	 * The active queue has requests and isn't expired, allow it to
 	 * dispatch.
 	 */

[PATCH] cfq-iosched: no need to keep track of busy_rt_queues

[Vivek Goyal]

Resending as had forgotten to put "[PATCH]" in subject line.

o Get rid of busy_rt_queues infrastructure. Looks like it is redundant.

o Once an RT queue gets request it will preempt any of the BE or IDLE queues
  immediately. Otherwise this queue will be put on service tree and scheduler
  will anyway select this queue before any of the BE or IDLE queue. Hence
  looks like there is no need to keep track of how many busy RT queues are
  currently on service tree. 

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
 block/cfq-iosched.c |   24 ------------------------
 1 file changed, 24 deletions(-)

Index: linux5/block/cfq-iosched.c
===================================================================
--- linux5.orig/block/cfq-iosched.c	2009-07-09 16:30:46.000000000 -0400
+++ linux5/block/cfq-iosched.c	2009-07-09 16:31:48.000000000 -0400
@@ -134,11 +134,6 @@ struct cfq_data {
 	struct rb_root prio_trees[CFQ_PRIO_LISTS];
 
 	unsigned int busy_queues;
-	/*
-	 * Used to track any pending rt requests so we can pre-empt current
-	 * non-RT cfqq in service when this value is non-zero.
-	 */
-	unsigned int busy_rt_queues;
 
 	int rq_in_driver;
 	int sync_flight;
@@ -648,9 +643,6 @@ static void cfq_add_cfqq_rr(struct cfq_d
 	BUG_ON(cfq_cfqq_on_rr(cfqq));
 	cfq_mark_cfqq_on_rr(cfqq);
 	cfqd->busy_queues++;
-	if (cfq_class_rt(cfqq))
-		cfqd->busy_rt_queues++;
-
 	cfq_resort_rr_list(cfqd, cfqq);
 }
 
@@ -673,8 +665,6 @@ static void cfq_del_cfqq_rr(struct cfq_d
 
 	BUG_ON(!cfqd->busy_queues);
 	cfqd->busy_queues--;
-	if (cfq_class_rt(cfqq))
-		cfqd->busy_rt_queues--;
 }
 
 /*
@@ -1179,20 +1169,6 @@ static struct cfq_queue *cfq_select_queu
 		goto expire;
 
 	/*
-	 * If we have a RT cfqq waiting, then we pre-empt the current non-rt
-	 * cfqq.
-	 */
-	if (!cfq_class_rt(cfqq) && cfqd->busy_rt_queues) {
-		/*
-		 * We simulate this as cfqq timed out so that it gets to bank
-		 * the remaining of its time slice.
-		 */
-		cfq_log_cfqq(cfqd, cfqq, "preempt");
-		cfq_slice_expired(cfqd, 1);
-		goto new_queue;
-	}
-
-	/*
 	 * The active queue has requests and isn't expired, allow it to
 	 * dispatch.
 	 */

Re: [PATCH] cfq-iosched: no need to keep track of busy_rt_queues

[Jens Axboe]

On Thu, Jul 09 2009, Vivek Goyal wrote:
> Resending as had forgotten to put "[PATCH]" in subject line.
> 
> o Get rid of busy_rt_queues infrastructure. Looks like it is redundant.
> 
> o Once an RT queue gets request it will preempt any of the BE or IDLE queues
>   immediately. Otherwise this queue will be put on service tree and scheduler
>   will anyway select this queue before any of the BE or IDLE queue. Hence
>   looks like there is no need to keep track of how many busy RT queues are
>   currently on service tree. 

Looks good, I'll queue this up for 2.6.32.

-- 
Jens Axboe

Re: [PATCH] cfq-iosched: no need to keep track of busy_rt_queues

[Divyesh Shah]

Change looks good to me too.

On Fri, Jul 10, 2009 at 1:18 AM, Jens Axboe<jens.axboe@oracle.com> wrote:
> On Thu, Jul 09 2009, Vivek Goyal wrote:
>> Resending as had forgotten to put "[PATCH]" in subject line.
>>
>> o Get rid of busy_rt_queues infrastructure. Looks like it is redundant.
>>
>> o Once an RT queue gets request it will preempt any of the BE or IDLE queues
>>   immediately. Otherwise this queue will be put on service tree and scheduler
>>   will anyway select this queue before any of the BE or IDLE queue. Hence
>>   looks like there is no need to keep track of how many busy RT queues are
>>   currently on service tree.
>
> Looks good, I'll queue this up for 2.6.32.
>
> --
> Jens Axboe
>
>