Commit 07b679f7 authored by Suwan Kim's avatar Suwan Kim Committed by Michael S. Tsirkin
Browse files

virtio-blk: support completion batching for the IRQ path 



This patch adds completion batching to the IRQ path. It reuses batch
completion code of virtblk_poll(). It collects requests to io_comp_batch
and processes them all at once. It can boost up the performance by 2%.

To validate the performance improvement and stabilty, I did fio test with
4 vCPU VM and 12 vCPU VM respectively. Both VMs have 8GB ram and the same
number of HW queues as vCPU.
The fio cammad is as follows and I ran the fio 5 times and got IOPS average.
(io_uring, randread, direct=1, bs=512, iodepth=64 numjobs=2,4)

Test result shows about 2% improvement.

           4 vcpu VM       |   numjobs=2   |   numjobs=4
      -----------------------------------------------------------
        fio without patch  |  367.2K IOPS  |   397.6K IOPS
      -----------------------------------------------------------
        fio with patch     |  372.8K IOPS  |   407.7K IOPS

           12 vcpu VM      |   numjobs=2   |   numjobs=4
      -----------------------------------------------------------
        fio without patch  |  363.6K IOPS  |   374.8K IOPS
      -----------------------------------------------------------
        fio with patch     |  373.8K IOPS  |   385.3K IOPS

Signed-off-by: default avatarSuwan Kim <suwan.kim027@gmail.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Message-Id: <20221221145456.281218-3-suwan.kim027@gmail.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 489e18f3

drivers/block/virtio_blk.c

+45 −37
Original line number Diff line number Diff line
@@ -334,33 +334,63 @@ static inline void virtblk_request_done(struct request *req) 
	blk_mq_end_request(req, status);

}



static void virtblk_complete_batch(struct io_comp_batch *iob)

{

	struct request *req;



	rq_list_for_each(&iob->req_list, req) {

		virtblk_unmap_data(req, blk_mq_rq_to_pdu(req));

		virtblk_cleanup_cmd(req);

	}

	blk_mq_end_request_batch(iob);

}



static int virtblk_handle_req(struct virtio_blk_vq *vq,

			      struct io_comp_batch *iob)

{

	struct virtblk_req *vbr;

	int req_done = 0;

	unsigned int len;



	while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {

		struct request *req = blk_mq_rq_from_pdu(vbr);



		if (likely(!blk_should_fake_timeout(req->q)) &&

		    !blk_mq_complete_request_remote(req) &&

		    !blk_mq_add_to_batch(req, iob, vbr->status,

					 virtblk_complete_batch))

			virtblk_request_done(req);

		req_done++;

	}



	return req_done;

}



static void virtblk_done(struct virtqueue *vq)

{

	struct virtio_blk *vblk = vq->vdev->priv;

	bool req_done = false;

	int qid = vq->index;

	struct virtblk_req *vbr;

	struct virtio_blk_vq *vblk_vq = &vblk->vqs[vq->index];

	int req_done = 0;

	unsigned long flags;

	unsigned int len;

	DEFINE_IO_COMP_BATCH(iob);



	spin_lock_irqsave(&vblk->vqs[qid].lock, flags);

	spin_lock_irqsave(&vblk_vq->lock, flags);

	do {

		virtqueue_disable_cb(vq);

		while ((vbr = virtqueue_get_buf(vblk->vqs[qid].vq, &len)) != NULL) {

			struct request *req = blk_mq_rq_from_pdu(vbr);

		req_done += virtblk_handle_req(vblk_vq, &iob);



			if (likely(!blk_should_fake_timeout(req->q)))

				blk_mq_complete_request(req);

			req_done = true;

		}

		if (unlikely(virtqueue_is_broken(vq)))

			break;

	} while (!virtqueue_enable_cb(vq));



	if (req_done) {

		if (!rq_list_empty(iob.req_list))

			iob.complete(&iob);



		/* In case queue is stopped waiting for more buffers. */

	if (req_done)

		blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);

	spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags);

	}

	spin_unlock_irqrestore(&vblk_vq->lock, flags);

}



static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx)
@@ -1176,37 +1206,15 @@ static void virtblk_map_queues(struct blk_mq_tag_set *set) 
	}

}



static void virtblk_complete_batch(struct io_comp_batch *iob)

{

	struct request *req;



	rq_list_for_each(&iob->req_list, req) {

		virtblk_unmap_data(req, blk_mq_rq_to_pdu(req));

		virtblk_cleanup_cmd(req);

	}

	blk_mq_end_request_batch(iob);

}



static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)

{

	struct virtio_blk *vblk = hctx->queue->queuedata;

	struct virtio_blk_vq *vq = get_virtio_blk_vq(hctx);

	struct virtblk_req *vbr;

	unsigned long flags;

	unsigned int len;

	int found = 0;



	spin_lock_irqsave(&vq->lock, flags);



	while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {

		struct request *req = blk_mq_rq_from_pdu(vbr);



		found++;

		if (!blk_mq_complete_request_remote(req) &&

		    !blk_mq_add_to_batch(req, iob, vbr->status,

						virtblk_complete_batch))

			virtblk_request_done(req);

	}

	found = virtblk_handle_req(vq, iob);



	if (found)

		blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);