[PATCH]block: don't delay blk_run_queue_async

[PATCH]block: don't delay blk_run_queue_async

[Shaohua Li]

Let's check a scenario:
1. blk_delay_queue(q, SCSI_QUEUE_DELAY);
2. blk_run_queue_async();
the second one will became a noop, because q->delay_work already has
WORK_STRUCT_PENDING_BIT set, so the delayed work will still run after
SCSI_QUEUE_DELAY. But blk_run_queue_async actually hopes the delayed
work runs immediately.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
---
 block/blk-core.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux/block/blk-core.c
===================================================================
--- linux.orig/block/blk-core.c	2011-05-18 16:17:54.000000000 +0800
+++ linux/block/blk-core.c	2011-05-18 16:29:38.000000000 +0800
@@ -316,8 +316,10 @@ EXPORT_SYMBOL(__blk_run_queue);
  */
 void blk_run_queue_async(struct request_queue *q)
 {
-	if (likely(!blk_queue_stopped(q)))
+	if (likely(!blk_queue_stopped(q))) {
+		__cancel_delayed_work(&q->delay_work);
 		queue_delayed_work(kblockd_workqueue, &q->delay_work, 0);
+	}
 }
 EXPORT_SYMBOL(blk_run_queue_async);
 

Re: [PATCH]block: don't delay blk_run_queue_async

[Jens Axboe]

On 2011-05-18 10:42, Shaohua Li wrote:
> Let's check a scenario:
> 1. blk_delay_queue(q, SCSI_QUEUE_DELAY);
> 2. blk_run_queue_async();
> the second one will became a noop, because q->delay_work already has
> WORK_STRUCT_PENDING_BIT set, so the delayed work will still run after
> SCSI_QUEUE_DELAY. But blk_run_queue_async actually hopes the delayed
> work runs immediately.

Good catch. I wonder if it wouldn't be better to "fix"
queue_delayed_work() instead. If the time passed in is before the
scheduled event, adjust the timeout.

But as a 2.6.39 fix, this is good, will queue up.

-- 
Jens Axboe