Re: [PATCH 1/1] virtio_blk: implement init_hctx MQ operation

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Aug 01, 2024 at 06:11:37PM +0300, Max Gurtovoy wrote:
> In this operation set the driver data of the hctx to point to the virtio
> block queue. By doing so, we can use this reference in the and reduce

in the .... ?

> the number of operations in the fast path.
> 
> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> ---
>  drivers/block/virtio_blk.c | 42 ++++++++++++++++++++------------------
>  1 file changed, 22 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 2351f411fa46..35a7a586f6f5 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -129,14 +129,6 @@ static inline blk_status_t virtblk_result(u8 status)
>  	}
>  }
>  
> -static inline struct virtio_blk_vq *get_virtio_blk_vq(struct blk_mq_hw_ctx *hctx)
> -{
> -	struct virtio_blk *vblk = hctx->queue->queuedata;
> -	struct virtio_blk_vq *vq = &vblk->vqs[hctx->queue_num];
> -
> -	return vq;
> -}
> -
>  static int virtblk_add_req(struct virtqueue *vq, struct virtblk_req *vbr)
>  {
>  	struct scatterlist out_hdr, in_hdr, *sgs[3];
> @@ -377,8 +369,7 @@ static void virtblk_done(struct virtqueue *vq)
>  
>  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 *vq = hctx->driver_data;
>  	bool kick;
>  
>  	spin_lock_irq(&vq->lock);
> @@ -428,10 +419,10 @@ 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 *vq = hctx->driver_data;
>  	struct request *req = bd->rq;
>  	struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
>  	unsigned long flags;
> -	int qid = hctx->queue_num;
>  	bool notify = false;
>  	blk_status_t status;
>  	int err;
> @@ -440,26 +431,26 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
>  	if (unlikely(status))
>  		return status;
>  
> -	spin_lock_irqsave(&vblk->vqs[qid].lock, flags);
> -	err = virtblk_add_req(vblk->vqs[qid].vq, vbr);
> +	spin_lock_irqsave(&vq->lock, flags);
> +	err = virtblk_add_req(vq->vq, vbr);
>  	if (err) {
> -		virtqueue_kick(vblk->vqs[qid].vq);
> +		virtqueue_kick(vq->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(&vq->lock, flags);
>  		virtblk_unmap_data(req, vbr);
>  		return virtblk_fail_to_queue(req, err);
>  	}
>  
> -	if (bd->last && virtqueue_kick_prepare(vblk->vqs[qid].vq))
> +	if (bd->last && virtqueue_kick_prepare(vq->vq))
>  		notify = true;
> -	spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags);
> +	spin_unlock_irqrestore(&vq->lock, flags);
>  
>  	if (notify)
> -		virtqueue_notify(vblk->vqs[qid].vq);
> +		virtqueue_notify(vq->vq);
>  	return BLK_STS_OK;
>  }
>  
> @@ -504,7 +495,7 @@ static void virtio_queue_rqs(struct request **rqlist)
>  	struct request *requeue_list = NULL;
>  
>  	rq_list_for_each_safe(rqlist, req, next) {
> -		struct virtio_blk_vq *vq = get_virtio_blk_vq(req->mq_hctx);
> +		struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
>  		bool kick;
>  
>  		if (!virtblk_prep_rq_batch(req)) {
> @@ -1164,6 +1155,16 @@ static const struct attribute_group *virtblk_attr_groups[] = {
>  	NULL,
>  };
>  
> +static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
> +		unsigned int hctx_idx)
> +{
> +	struct virtio_blk *vblk = data;
> +	struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
> +
> +	hctx->driver_data = vq;
> +	return 0;
> +}
> +
>  static void virtblk_map_queues(struct blk_mq_tag_set *set)
>  {
>  	struct virtio_blk *vblk = set->driver_data;
> @@ -1205,7 +1206,7 @@ static void virtblk_complete_batch(struct io_comp_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 virtio_blk_vq *vq = hctx->driver_data;
>  	struct virtblk_req *vbr;
>  	unsigned long flags;
>  	unsigned int len;
> @@ -1236,6 +1237,7 @@ static const struct blk_mq_ops virtio_mq_ops = {
>  	.queue_rqs	= virtio_queue_rqs,
>  	.commit_rqs	= virtio_commit_rqs,
>  	.complete	= virtblk_request_done,
> +	.init_hctx	= virtblk_init_hctx,
>  	.map_queues	= virtblk_map_queues,
>  	.poll		= virtblk_poll,
>  };
> -- 
> 2.18.1