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block: drop queue lock before calling __blk_run_queue() for kblockd punt

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If we know we are going to punt to kblockd, we can drop the queue
lock before calling into __blk_run_queue() since it only does a
safe bit test and a workqueue call. Since kblockd needs to grab
this very lock as one of the first things it does, it's a good
optimization to drop the lock before waking kblockd.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Jens Axboe 2011-04-18 09:59:55 +02:00
parent b4cb290e0a
commit 99e22598e9
1 changed files with 25 additions and 8 deletions
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33
block/blk-core.c
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@ -295,7 +295,8 @@ EXPORT_SYMBOL(blk_sync_queue);
*
* Description:
* See @blk_run_queue. This variant must be called with the queue lock
* held and interrupts disabled.
* held and interrupts disabled. If force_kblockd is true, then it is
* safe to call this without holding the queue lock.
*
*/
void __blk_run_queue(struct request_queue *q, bool force_kblockd)
@ -2671,9 +2672,23 @@ static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
*/
static void queue_unplugged(struct request_queue *q, unsigned int depth,
bool from_schedule)
__releases(q->queue_lock)
{
trace_block_unplug(q, depth, !from_schedule);
__blk_run_queue(q, from_schedule);
/*
* If we are punting this to kblockd, then we can safely drop
* the queue_lock before waking kblockd (which needs to take
* this lock).
*/
if (from_schedule) {
spin_unlock(q->queue_lock);
__blk_run_queue(q, true);
} else {
__blk_run_queue(q, false);
spin_unlock(q->queue_lock);
}
}
static void flush_plug_callbacks(struct blk_plug *plug)
@ -2729,10 +2744,11 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
BUG_ON(!(rq->cmd_flags & REQ_ON_PLUG));
BUG_ON(!rq->q);
if (rq->q != q) {
if (q) {
/*
* This drops the queue lock
*/
if (q)
queue_unplugged(q, depth, from_schedule);
spin_unlock(q->queue_lock);
}
q = rq->q;
depth = 0;
spin_lock(q->queue_lock);
@ -2750,10 +2766,11 @@ void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
depth++;
}
if (q) {
/*
* This drops the queue lock
*/
if (q)
queue_unplugged(q, depth, from_schedule);
spin_unlock(q->queue_lock);
}
local_irq_restore(flags);
}