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Commit 27419322 authored by Shaohua Li's avatar Shaohua Li Committed by Jens Axboe
Browse files

block: recursive merge requests 



In my 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.
With recursive merge below, the workload throughput gets improved 20%
and context switch drops 60%.

Signed-off-by: default avatarShaohua Li <shaohua.li@intel.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 4a0b75c7

block/elevator.c

+12 −4
Original line number Original line Diff line number Diff line
@@ -515,6 +515,7 @@ static bool elv_attempt_insert_merge(struct request_queue *q, 
				     struct request *rq)

				     struct request *rq)

{

{

	struct request *__rq;

	struct request *__rq;

	bool ret;





	if (blk_queue_nomerges(q))

	if (blk_queue_nomerges(q))

		return false;

		return false;
@@ -528,14 +529,21 @@ static bool elv_attempt_insert_merge(struct request_queue *q, 
	if (blk_queue_noxmerges(q))

	if (blk_queue_noxmerges(q))

		return false;

		return false;





	ret = false;

	/*

	/*

	 * See if our hash lookup can find a potential backmerge.

	 * See if our hash lookup can find a potential backmerge.

	 */

	 */

	while (1) {

		__rq = elv_rqhash_find(q, blk_rq_pos(rq));

		__rq = elv_rqhash_find(q, blk_rq_pos(rq));

	if (__rq && blk_attempt_req_merge(q, __rq, rq))

		if (!__rq || !blk_attempt_req_merge(q, __rq, rq))

		return true;

			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)

void elv_merged_request(struct request_queue *q, struct request *rq, int type)