block: recursive merge requests (27419322) · Commits · 戴 / test

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:

Shaohua Li <shaohua.li@intel.com> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

block/elevator.c

+12 −4

Original line number	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;
		bool ret;

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

		ret = false;
		/*
		* See if our hash lookup can find a potential backmerge.
		*/
		while (1) {
		__rq = elv_rqhash_find(q, blk_rq_pos(rq));
		if (__rq && blk_attempt_req_merge(q, __rq, rq))
		return true;
		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)

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