From: Jens Axboe <axboe@suse.de>
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>
---
25-akpm/drivers/block/noop-iosched.c | 27 +++------------------------
1 files changed, 3 insertions(+), 24 deletions(-)
diff -puN drivers/block/noop-iosched.c~noop-iosched-kill-on-merge-scan drivers/block/noop-iosched.c
--- 25/drivers/block/noop-iosched.c~noop-iosched-kill-on-merge-scan 2005-04-13 00:56:45.975952040 -0700
+++ 25-akpm/drivers/block/noop-iosched.c 2005-04-13 00:56:45.978951584 -0700
@@ -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,
_