linux-kernel - [PATCH 2/3] virtio_blk: avoid repeating vblk->vqs[qid]

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Date:   Thu, 20 May 2021 15:13:04 +0100
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     virtualization@...ts.linux-foundation.org
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Jason Wang <jasowang@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, slp@...hat.com,
        sgarzare@...hat.com, "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: [PATCH 2/3] virtio_blk: avoid repeating vblk->vqs[qid]

struct virtio_blk_vq is accessed in many places. Introduce "vbq" local
variables to avoid repeating vblk->vqs[qid] throughout the code. The
patches that follow will add more accesses, making the payoff even
greater.

virtio_commit_rqs() calls the local variable "vq", which is easily
confused with struct virtqueue. Rename to "vbq" for clarity.

Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>
---
 drivers/block/virtio_blk.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index b9fa3ef5b57c..fc0fb1dcd399 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -174,16 +174,16 @@ static inline void virtblk_request_done(struct request *req)
 static void virtblk_done(struct virtqueue *vq)
 {
 	struct virtio_blk *vblk = vq->vdev->priv;
+	struct virtio_blk_vq *vbq = &vblk->vqs[vq->index];
 	bool req_done = false;
-	int qid = vq->index;
 	struct virtblk_req *vbr;
 	unsigned long flags;
 	unsigned int len;
 
-	spin_lock_irqsave(&vblk->vqs[qid].lock, flags);
+	spin_lock_irqsave(&vbq->lock, flags);
 	do {
 		virtqueue_disable_cb(vq);
-		while ((vbr = virtqueue_get_buf(vblk->vqs[qid].vq, &len)) != NULL) {
+		while ((vbr = virtqueue_get_buf(vq, &len)) != NULL) {
 			struct request *req = blk_mq_rq_from_pdu(vbr);
 
 			if (likely(!blk_should_fake_timeout(req->q)))
@@ -197,32 +197,32 @@ static void virtblk_done(struct virtqueue *vq)
 	/* 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(&vbq->lock, flags);
 }
 
 static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx)
 {
 	struct virtio_blk *vblk = hctx->queue->queuedata;
-	struct virtio_blk_vq *vq = &vblk->vqs[hctx->queue_num];
+	struct virtio_blk_vq *vbq = &vblk->vqs[hctx->queue_num];
 	bool kick;
 
-	spin_lock_irq(&vq->lock);
-	kick = virtqueue_kick_prepare(vq->vq);
-	spin_unlock_irq(&vq->lock);
+	spin_lock_irq(&vbq->lock);
+	kick = virtqueue_kick_prepare(vbq->vq);
+	spin_unlock_irq(&vbq->lock);
 
 	if (kick)
-		virtqueue_notify(vq->vq);
+		virtqueue_notify(vbq->vq);
 }
 
 static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
 			   const struct blk_mq_queue_data *bd)
 {
 	struct virtio_blk *vblk = hctx->queue->queuedata;
+	struct virtio_blk_vq *vbq = &vblk->vqs[hctx->queue_num];
 	struct request *req = bd->rq;
 	struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
 	unsigned long flags;
 	unsigned int num;
-	int qid = hctx->queue_num;
 	int err;
 	bool notify = false;
 	bool unmap = false;
@@ -274,16 +274,16 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
 			vbr->out_hdr.type |= cpu_to_virtio32(vblk->vdev, VIRTIO_BLK_T_IN);
 	}
 
-	spin_lock_irqsave(&vblk->vqs[qid].lock, flags);
-	err = virtblk_add_req(vblk->vqs[qid].vq, vbr, vbr->sg, num);
+	spin_lock_irqsave(&vbq->lock, flags);
+	err = virtblk_add_req(vbq->vq, vbr, vbr->sg, num);
 	if (err) {
-		virtqueue_kick(vblk->vqs[qid].vq);
+		virtqueue_kick(vbq->vq);
 		/* Don't stop the queue if -ENOMEM: we may have failed to
 		 * bounce the buffer due to global resource outage.
 		 */
 		if (err == -ENOSPC)
 			blk_mq_stop_hw_queue(hctx);
-		spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags);
+		spin_unlock_irqrestore(&vbq->lock, flags);
 		switch (err) {
 		case -ENOSPC:
 			return BLK_STS_DEV_RESOURCE;
@@ -294,12 +294,12 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
 		}
 	}
 
-	if (bd->last && virtqueue_kick_prepare(vblk->vqs[qid].vq))
+	if (bd->last && virtqueue_kick_prepare(vbq->vq))
 		notify = true;
-	spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags);
+	spin_unlock_irqrestore(&vbq->lock, flags);
 
 	if (notify)
-		virtqueue_notify(vblk->vqs[qid].vq);
+		virtqueue_notify(vbq->vq);
 	return BLK_STS_OK;
 }
 
-- 
2.31.1