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[PATCH] noop-iosched: kill O(N) merge scan

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Profiling hit rates on merging shows that the last merge hint works
extremely well for most work loads.  So lets kill the linear merge scan in
noop-iosched, so it provides O(1) run time for any operation.

Testing credits go to Ken Chen from Intel.

Signed-off-by: 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:
Jens Axboe 2005-05-01 08:59:06 -07:00 committed by Linus Torvalds
parent 41f11a4fa3
commit 1181c1f923
1 changed files with 3 additions and 24 deletions
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27
drivers/block/noop-iosched.c
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@ -13,34 +13,13 @@
static int elevator_noop_merge(request_queue_t *q, struct request **req,
struct bio *bio)
{
struct list_head *entry = &q->queue_head;
struct request *__rq;
int ret;
if ((ret = elv_try_last_merge(q, bio))) {
ret = elv_try_last_merge(q, bio);
if (ret != ELEVATOR_NO_MERGE)
*req = q->last_merge;
return ret;
}
while ((entry = entry->prev) != &q->queue_head) {
__rq = list_entry_rq(entry);
if (__rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER))
break;
else if (__rq->flags & REQ_STARTED)
break;
if (!blk_fs_request(__rq))
continue;
if ((ret = elv_try_merge(__rq, bio))) {
*req = __rq;
q->last_merge = __rq;
return ret;
}
}
return ELEVATOR_NO_MERGE;
return ret;
}
static void elevator_noop_merge_requests(request_queue_t *q, struct request *req,