[PATCH] blk: reduce locking
Change around locking a bit for a result of 1-2 less spin lock unlock pairs in
request submission paths.
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/block/ll_rw_blk.c b/drivers/block/ll_rw_blk.c
index 67431f2..5caebe2 100644
--- a/drivers/block/ll_rw_blk.c
+++ b/drivers/block/ll_rw_blk.c
@@ -1867,19 +1867,20 @@
#define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
/*
- * Get a free request, queue_lock must not be held
+ * Get a free request, queue_lock must be held.
+ * Returns NULL on failure, with queue_lock held.
+ * Returns !NULL on success, with queue_lock *not held*.
*/
static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
int gfp_mask)
{
struct request *rq = NULL;
struct request_list *rl = &q->rq;
- struct io_context *ioc = get_io_context(gfp_mask);
+ struct io_context *ioc = get_io_context(GFP_ATOMIC);
if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)))
goto out;
- spin_lock_irq(q->queue_lock);
if (rl->count[rw]+1 >= q->nr_requests) {
/*
* The queue will fill after this allocation, so set it as
@@ -1907,7 +1908,6 @@
* The queue is full and the allocating process is not a
* "batcher", and not exempted by the IO scheduler
*/
- spin_unlock_irq(q->queue_lock);
goto out;
}
@@ -1950,7 +1950,6 @@
if (unlikely(rl->count[rw] == 0))
rl->starved[rw] = 1;
- spin_unlock_irq(q->queue_lock);
goto out;
}
@@ -1967,6 +1966,8 @@
/*
* No available requests for this queue, unplug the device and wait for some
* requests to become available.
+ *
+ * Called with q->queue_lock held, and returns with it unlocked.
*/
static struct request *get_request_wait(request_queue_t *q, int rw,
struct bio *bio)
@@ -1986,7 +1987,8 @@
if (!rq) {
struct io_context *ioc;
- generic_unplug_device(q);
+ __generic_unplug_device(q);
+ spin_unlock_irq(q->queue_lock);
io_schedule();
/*
@@ -1998,6 +2000,8 @@
ioc = get_io_context(GFP_NOIO);
ioc_set_batching(q, ioc);
put_io_context(ioc);
+
+ spin_lock_irq(q->queue_lock);
}
finish_wait(&rl->wait[rw], &wait);
}
@@ -2011,14 +2015,18 @@
BUG_ON(rw != READ && rw != WRITE);
- if (gfp_mask & __GFP_WAIT)
+ spin_lock_irq(q->queue_lock);
+ if (gfp_mask & __GFP_WAIT) {
rq = get_request_wait(q, rw, NULL);
- else
+ } else {
rq = get_request(q, rw, NULL, gfp_mask);
+ if (!rq)
+ spin_unlock_irq(q->queue_lock);
+ }
+ /* q->queue_lock is unlocked at this point */
return rq;
}
-
EXPORT_SYMBOL(blk_get_request);
/**
@@ -2605,9 +2613,10 @@
get_rq:
/*
* Grab a free request. This is might sleep but can not fail.
+ * Returns with the queue unlocked.
*/
- spin_unlock_irq(q->queue_lock);
req = get_request_wait(q, rw, bio);
+
/*
* After dropping the lock and possibly sleeping here, our request
* may now be mergeable after it had proven unmergeable (above).