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[PATCH] blk: __make_request efficiency

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In the case where the request is not able to be merged by the elevator, don't
retake the lock and retry the merge mechanism after allocating a new request.

Instead assume that the chance of a merge remains slim, and now that we've
done most of the work allocating a request we may as well just go with it.

Also be rid of the GFP_ATOMIC allocation: we've got working mempools for the
block layer now, so let's save atomic memory for things like networking.

Lastly, in get_request_wait, do an initial get_request call before going into
the waitqueue.  This is reported to help efficiency.

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 20:45:13 -07:00 committed by Linus Torvalds
parent 69f63c5c34
commit 450991bc10
1 changed files with 22 additions and 42 deletions
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64
drivers/block/ll_rw_blk.c
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@ -1971,10 +1971,11 @@ static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
static struct request *get_request_wait(request_queue_t *q, int rw,
struct bio *bio)
{
DEFINE_WAIT(wait);
struct request *rq;
do {
rq = get_request(q, rw, bio, GFP_NOIO);
while (!rq) {
DEFINE_WAIT(wait);
struct request_list *rl = &q->rq;
prepare_to_wait_exclusive(&rl->wait[rw], &wait,
@ -1999,7 +2000,7 @@ static struct request *get_request_wait(request_queue_t *q, int rw,
put_io_context(ioc);
}
finish_wait(&rl->wait[rw], &wait);
} while (!rq);
}
return rq;
}
@ -2521,7 +2522,7 @@ EXPORT_SYMBOL(blk_attempt_remerge);
static int __make_request(request_queue_t *q, struct bio *bio)
{
struct request *req, *freereq = NULL;
struct request *req;
int el_ret, rw, nr_sectors, cur_nr_sectors, barrier, err, sync;
unsigned short prio;
sector_t sector;
@ -2549,14 +2550,9 @@ static int __make_request(request_queue_t *q, struct bio *bio)
goto end_io;
}
again:
spin_lock_irq(q->queue_lock);
if (elv_queue_empty(q)) {
blk_plug_device(q);
goto get_rq;
}
if (barrier)
if (unlikely(barrier) || elv_queue_empty(q))
goto get_rq;
el_ret = elv_merge(q, &req, bio);
@ -2601,40 +2597,23 @@ static int __make_request(request_queue_t *q, struct bio *bio)
elv_merged_request(q, req);
goto out;
/*
* elevator says don't/can't merge. get new request
*/
case ELEVATOR_NO_MERGE:
break;
/* ELV_NO_MERGE: elevator says don't/can't merge. */
default:
printk("elevator returned crap (%d)\n", el_ret);
BUG();
;
}
/*
* Grab a free request from the freelist - if that is empty, check
* if we are doing read ahead and abort instead of blocking for
* a free slot.
*/
get_rq:
if (freereq) {
req = freereq;
freereq = NULL;
} else {
spin_unlock_irq(q->queue_lock);
if ((freereq = get_request(q, rw, bio, GFP_ATOMIC)) == NULL) {
/*
* READA bit set
*/
err = -EWOULDBLOCK;
if (bio_rw_ahead(bio))
goto end_io;
freereq = get_request_wait(q, rw, bio);
}
goto again;
}
/*
* Grab a free request. This is might sleep but can not fail.
*/
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).
* We don't worry about that case for efficiency. It won't happen
* often, and the elevators are able to handle it.
*/
req->flags |= REQ_CMD;
@ -2663,10 +2642,11 @@ static int __make_request(request_queue_t *q, struct bio *bio)
req->rq_disk = bio->bi_bdev->bd_disk;
req->start_time = jiffies;
spin_lock_irq(q->queue_lock);
if (elv_queue_empty(q))
blk_plug_device(q);
add_request(q, req);
out:
if (freereq)
__blk_put_request(q, freereq);
if (sync)
__generic_unplug_device(q);