CFQ ioprio setting patch

CFQ ioprio setting patch

[Vasily Tarasov]

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If you set io-priority of process 1 using sys_ioprio_set system call by 
another process 2 (like ionice do),
then cfq_init_prio_data() function sets priority of process 2 (current) 
on queue of process 1 and clears the flag, that designates change of ioprio.
So the process  1 will work like with priority of process 2.

I propose not to call cfq_init_prio_data() on io-priority change, but 
only mark queue as queue with changed prority.
Every time when new request comes cfq-scheduler checks for this flag and 
atomaticaly changes priority of queue to new value.

Small patch is below.

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--- linux-2.6.16-026stab012-ioprio/block/cfq-iosched.c.orig	2006-05-29 13:46:20.000000000 +0400
+++ linux-2.6.16-026stab012-ioprio/block/cfq-iosched.c	2006-05-24 15:31:24.000000000 +0400
@@ -1325,7 +1325,6 @@ static inline void changed_ioprio(struct
 
 		spin_lock(cfqd->queue->queue_lock);
 		cfq_mark_cfqq_prio_changed(cfqq);
-		cfq_init_prio_data(cfqq);
 		spin_unlock(cfqd->queue->queue_lock);
 	}
 }

Re: CFQ ioprio setting patch

[Jens Axboe]

On Wed, May 24 2006, Vasily Tarasov wrote:
> If you set io-priority of process 1 using sys_ioprio_set system call by 
> another process 2 (like ionice do),
> then cfq_init_prio_data() function sets priority of process 2 (current) 
> on queue of process 1 and clears the flag, that designates change of ioprio.
> So the process  1 will work like with priority of process 2.
> 
> I propose not to call cfq_init_prio_data() on io-priority change, but 
> only mark queue as queue with changed prority.
> Every time when new request comes cfq-scheduler checks for this flag and 
> atomaticaly changes priority of queue to new value.

Your analysis looks correct. However the patch is not -stable material,
I've queued it for inclusion post 2.6.17, thanks. Newer version below
for 2.6.17-rc6. If you have the time, please test that 2.6.17-rc6 has
the same bug and that this patch (which is just a port of yours) does
fix it.

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 56bec4e..e636b0f 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1400,10 +1400,9 @@ static inline void changed_ioprio(struct
 			}
 		}
 		cfqq = cic->cfqq[SYNC];
-		if (cfqq) {
+		if (cfqq)
 			cfq_mark_cfqq_prio_changed(cfqq);
-			cfq_init_prio_data(cfqq);
-		}
+
 		spin_unlock(cfqd->queue->queue_lock);
 	}
 }

-- 
Jens Axboe