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

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Date:   Tue, 25 May 2021 10:25:16 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Stefan Hajnoczi <stefanha@...hat.com>,
        virtualization@...ts.linux-foundation.org
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, slp@...hat.com,
        sgarzare@...hat.com, "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH 2/3] virtio_blk: avoid repeating vblk->vqs[qid]


在 2021/5/20 下午10:13, Stefan Hajnoczi 写道:
> 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>


Acked-by: Jason Wang <jasowang@...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;
>   }
>