Commit ab42f35d authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

blk-mq: merge bio into sw queue before plugging 



Before blk-mq is introduced, I/O is merged to elevator
before being putted into plug queue, but blk-mq changed the
order and makes merging to sw queue basically impossible.
Then it is observed that throughput of sequential I/O is degraded
about 10%~20% on virtio-blk in the test[1] if mq-deadline isn't used.

This patch moves the bio merging per sw queue before plugging,
like what blk_queue_bio() does, and the performance regression is
fixed under this situation.

[1]. test script:
sudo fio --direct=1 --size=128G --bsrange=4k-4k --runtime=40 --numjobs=16 --ioengine=libaio --iodepth=64 --group_reporting=1 --filename=/dev/vdb --name=virtio_blk-test-$RW --rw=$RW --output-format=json

RW=read or write

Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent cdbe0206

block/blk-mq.c

+26 −22
Original line number Diff line number Diff line
@@ -1427,30 +1427,30 @@ static inline bool hctx_allow_merges(struct blk_mq_hw_ctx *hctx) 
		!blk_queue_nomerges(hctx->queue);

}



static inline bool blk_mq_merge_queue_io(struct blk_mq_hw_ctx *hctx,

					 struct blk_mq_ctx *ctx,

					 struct request *rq, struct bio *bio)

/* attempt to merge bio into current sw queue */

static inline bool blk_mq_merge_bio(struct request_queue *q, struct bio *bio)

{

	if (!hctx_allow_merges(hctx) || !bio_mergeable(bio)) {

		blk_mq_bio_to_request(rq, bio);

	bool ret = false;

	struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);

	struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);



	if (hctx_allow_merges(hctx) && bio_mergeable(bio)) {

		spin_lock(&ctx->lock);

insert_rq:

		__blk_mq_insert_request(hctx, rq, false);

		ret = blk_mq_attempt_merge(q, ctx, bio);

		spin_unlock(&ctx->lock);

		return false;

	} else {

		struct request_queue *q = hctx->queue;

	}



		spin_lock(&ctx->lock);

		if (!blk_mq_attempt_merge(q, ctx, bio)) {

			blk_mq_bio_to_request(rq, bio);

			goto insert_rq;

	blk_mq_put_ctx(ctx);

	return ret;

}



static inline void blk_mq_queue_io(struct blk_mq_hw_ctx *hctx,

				   struct blk_mq_ctx *ctx,

				   struct request *rq)

{

	spin_lock(&ctx->lock);

	__blk_mq_insert_request(hctx, rq, false);

	spin_unlock(&ctx->lock);

		__blk_mq_finish_request(hctx, ctx, rq);

		return true;

	}

}



static blk_qc_t request_to_qc_t(struct blk_mq_hw_ctx *hctx, struct request *rq)
@@ -1549,6 +1549,9 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio) 
	if (blk_mq_sched_bio_merge(q, bio))

		return BLK_QC_T_NONE;



	if (blk_mq_merge_bio(q, bio))

		return BLK_QC_T_NONE;



	wb_acct = wbt_wait(q->rq_wb, bio, NULL);



	trace_block_getrq(q, bio, bio->bi_opf);
@@ -1630,11 +1633,12 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio) 
		blk_mq_put_ctx(data.ctx);

		blk_mq_bio_to_request(rq, bio);

		blk_mq_sched_insert_request(rq, false, true, true, true);

	} else if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {

	} else {

		blk_mq_put_ctx(data.ctx);

		blk_mq_bio_to_request(rq, bio);

		blk_mq_queue_io(data.hctx, data.ctx, rq);

		blk_mq_run_hw_queue(data.hctx, true);

	} else

		blk_mq_put_ctx(data.ctx);

	}



	return cookie;

}

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