block: recursive merge requests
In a workload, thread 1 accesses a, a+2, ..., thread 2 accesses a+1, a+3,....
When the requests are flushed to queue, a and a+1 are merged to (a, a+1), a+2
and a+3 too to (a+2, a+3), but (a, a+1) and (a+2, a+3) aren't merged.
If we do recursive merge for such interleave access, some workloads throughput
get improvement. A recent worload I'm checking on is swap, below change
boostes the throughput around 5% ~ 10%.
Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/elevator.c b/block/elevator.c
index 9b1d42b..9edba1b 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -458,6 +458,7 @@
struct request *rq)
{
struct request *__rq;
+ bool ret;
if (blk_queue_nomerges(q))
return false;
@@ -471,14 +472,21 @@
if (blk_queue_noxmerges(q))
return false;
+ ret = false;
/*
* See if our hash lookup can find a potential backmerge.
*/
- __rq = elv_rqhash_find(q, blk_rq_pos(rq));
- if (__rq && blk_attempt_req_merge(q, __rq, rq))
- return true;
+ while (1) {
+ __rq = elv_rqhash_find(q, blk_rq_pos(rq));
+ if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
+ break;
- return false;
+ /* The merged request could be merged with others, try again */
+ ret = true;
+ rq = __rq;
+ }
+
+ return ret;
}
void elv_merged_request(struct request_queue *q, struct request *rq, int type)