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[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>
This commit is contained in:
Nick Piggin 2005-06-28 20:45:14 -07:00 committed by Linus Torvalds
parent 450991bc10
commit d6344532a2
1 changed files with 19 additions and 10 deletions
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29
drivers/block/ll_rw_blk.c
View File

@ -1867,19 +1867,20 @@ static void freed_request(request_queue_t *q, int rw)
#define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist) #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, static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
int gfp_mask) int gfp_mask)
{ {
struct request *rq = NULL; struct request *rq = NULL;
struct request_list *rl = &q->rq; 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))) if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)))
goto out; goto out;
spin_lock_irq(q->queue_lock);
if (rl->count[rw]+1 >= q->nr_requests) { if (rl->count[rw]+1 >= q->nr_requests) {
/* /*
* The queue will fill after this allocation, so set it as * The queue will fill after this allocation, so set it as
@ -1907,7 +1908,6 @@ static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
* The queue is full and the allocating process is not a * The queue is full and the allocating process is not a
* "batcher", and not exempted by the IO scheduler * "batcher", and not exempted by the IO scheduler
*/ */
spin_unlock_irq(q->queue_lock);
goto out; goto out;
} }
@ -1950,7 +1950,6 @@ rq_starved:
if (unlikely(rl->count[rw] == 0)) if (unlikely(rl->count[rw] == 0))
rl->starved[rw] = 1; rl->starved[rw] = 1;
spin_unlock_irq(q->queue_lock);
goto out; goto out;
} }
@ -1967,6 +1966,8 @@ out:
/* /*
* No available requests for this queue, unplug the device and wait for some * No available requests for this queue, unplug the device and wait for some
* requests to become available. * 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, static struct request *get_request_wait(request_queue_t *q, int rw,
struct bio *bio) struct bio *bio)
@ -1986,7 +1987,8 @@ static struct request *get_request_wait(request_queue_t *q, int rw,
if (!rq) { if (!rq) {
struct io_context *ioc; struct io_context *ioc;
generic_unplug_device(q); __generic_unplug_device(q);
spin_unlock_irq(q->queue_lock);
io_schedule(); io_schedule();
/* /*
@ -1998,6 +2000,8 @@ static struct request *get_request_wait(request_queue_t *q, int rw,
ioc = get_io_context(GFP_NOIO); ioc = get_io_context(GFP_NOIO);
ioc_set_batching(q, ioc); ioc_set_batching(q, ioc);
put_io_context(ioc); put_io_context(ioc);
spin_lock_irq(q->queue_lock);
} }
finish_wait(&rl->wait[rw], &wait); finish_wait(&rl->wait[rw], &wait);
} }
@ -2011,14 +2015,18 @@ struct request *blk_get_request(request_queue_t *q, int rw, int gfp_mask)
BUG_ON(rw != READ && rw != WRITE); 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); rq = get_request_wait(q, rw, NULL);
else } else {
rq = get_request(q, rw, NULL, gfp_mask); 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; return rq;
} }
EXPORT_SYMBOL(blk_get_request); EXPORT_SYMBOL(blk_get_request);
/** /**
@ -2605,9 +2613,10 @@ static int __make_request(request_queue_t *q, struct bio *bio)
get_rq: get_rq:
/* /*
* Grab a free request. This is might sleep but can not fail. * 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); req = get_request_wait(q, rw, bio);
/* /*
* After dropping the lock and possibly sleeping here, our request * After dropping the lock and possibly sleeping here, our request
* may now be mergeable after it had proven unmergeable (above). * may now be mergeable after it had proven unmergeable (above).