Re: [PATCH 2/2] virtio_scsi: implement request batching

Ming Lei
2019-07-08T09:48:14Z

On Thu, May 30, 2019 at 7:28 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> Adding the command and kicking the virtqueue so far was done one after
> another. Make the kick optional, so that we can take into account SCMD_LAST.
> We also need a commit_rqs callback to kick the device if blk-mq aborts
> the submission before the last request is reached.
>
> Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> drivers/scsi/virtio_scsi.c | 55 +++++++++++++++++++++++++++-----------
> 1 file changed, 40 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> index 8af01777d09c..918c811cea95 100644
> --- a/drivers/scsi/virtio_scsi.c
> +++ b/drivers/scsi/virtio_scsi.c
> @@ -375,14 +375,7 @@ static void virtscsi_event_done(struct virtqueue *vq)
> virtscsi_vq_done(vscsi, &vscsi->event_vq, virtscsi_complete_event);
> };
>
> -/**
> - * virtscsi_add_cmd - add a virtio_scsi_cmd to a virtqueue
> - * @vq : the struct virtqueue we're talking about
> - * @cmd : command structure
> - * @req_size : size of the request buffer
> - * @resp_size : size of the response buffer
> - */
> -static int virtscsi_add_cmd(struct virtqueue *vq,
> +static int __virtscsi_add_cmd(struct virtqueue *vq,
> struct virtio_scsi_cmd *cmd,
> size_t req_size, size_t resp_size)
> {
> @@ -427,17 +420,39 @@ static int virtscsi_add_cmd(struct virtqueue *vq,
> return virtqueue_add_sgs(vq, sgs, out_num, in_num, cmd, GFP_ATOMIC);
> }
>
> -static int virtscsi_kick_cmd(struct virtio_scsi_vq *vq,
> +static void virtscsi_kick_vq(struct virtio_scsi_vq *vq)
> +{
> + bool needs_kick;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&vq->vq_lock, flags);
> + needs_kick = virtqueue_kick_prepare(vq->vq);
> + spin_unlock_irqrestore(&vq->vq_lock, flags);
> +
> + if (needs_kick)
> + virtqueue_notify(vq->vq);
> +}
> +
> +/**
> + * virtscsi_add_cmd - add a virtio_scsi_cmd to a virtqueue, optionally kick it
> + * @vq : the struct virtqueue we're talking about
> + * @cmd : command structure
> + * @req_size : size of the request buffer
> + * @resp_size : size of the response buffer
> + * @kick : whether to kick the virtqueue immediately
> + */
> +static int virtscsi_add_cmd(struct virtio_scsi_vq *vq,
> struct virtio_scsi_cmd *cmd,
> - size_t req_size, size_t resp_size)
> + size_t req_size, size_t resp_size,
> + bool kick)
> {
> unsigned long flags;
> int err;
> bool needs_kick = false;
>
> spin_lock_irqsave(&vq->vq_lock, flags);
> - err = virtscsi_add_cmd(vq->vq, cmd, req_size, resp_size);
> - if (!err)
> + err = __virtscsi_add_cmd(vq->vq, cmd, req_size, resp_size);
> + if (!err && kick)
> needs_kick = virtqueue_kick_prepare(vq->vq);
>
> spin_unlock_irqrestore(&vq->vq_lock, flags);
> @@ -502,6 +517,7 @@ static int virtscsi_queuecommand(struct Scsi_Host *shost,
> struct virtio_scsi *vscsi = shost_priv(shost);
> struct virtio_scsi_vq *req_vq = virtscsi_pick_vq_mq(vscsi, sc);
> struct virtio_scsi_cmd *cmd = scsi_cmd_priv(sc);
> + bool kick;
> unsigned long flags;
> int req_size;
> int ret;
> @@ -531,7 +547,8 @@ static int virtscsi_queuecommand(struct Scsi_Host *shost,
> req_size = sizeof(cmd->req.cmd);
> }
>
> - ret = virtscsi_kick_cmd(req_vq, cmd, req_size, sizeof(cmd->resp.cmd));
> + kick = (sc->flags & SCMD_LAST) != 0;
> + ret = virtscsi_add_cmd(req_vq, cmd, req_size, sizeof(cmd->resp.cmd), kick);
> if (ret == -EIO) {
> cmd->resp.cmd.response = VIRTIO_SCSI_S_BAD_TARGET;
> spin_lock_irqsave(&req_vq->vq_lock, flags);
> @@ -549,8 +566,8 @@ static int virtscsi_tmf(struct virtio_scsi *vscsi, struct virtio_scsi_cmd *cmd)
> int ret = FAILED;
>
> cmd->comp = &comp;
> - if (virtscsi_kick_cmd(&vscsi->ctrl_vq, cmd,
> - sizeof cmd->req.tmf, sizeof cmd->resp.tmf) < 0)
> + if (virtscsi_add_cmd(&vscsi->ctrl_vq, cmd,
> + sizeof cmd->req.tmf, sizeof cmd->resp.tmf, true) < 0)
> goto out;
>
> wait_for_completion(&comp);
> @@ -664,6 +681,13 @@ static int virtscsi_map_queues(struct Scsi_Host *shost)
> return blk_mq_virtio_map_queues(qmap, vscsi->vdev, 2);
> }
>
> +static void virtscsi_commit_rqs(struct Scsi_Host *shost, u16 hwq)
> +{
> + struct virtio_scsi *vscsi = shost_priv(shost);
> +
> + virtscsi_kick_vq(&vscsi->req_vqs[hwq]);
> +}
> +
> /*
> * The host guarantees to respond to each command, although I/O
> * latencies might be higher than on bare metal. Reset the timer
> @@ -681,6 +705,7 @@ static struct scsi_host_template virtscsi_host_template = {
> .this_id = -1,
> .cmd_size = sizeof(struct virtio_scsi_cmd),
> .queuecommand = virtscsi_queuecommand,
> + .commit_rqs = virtscsi_commit_rqs,
> .change_queue_depth = virtscsi_change_queue_depth,
> .eh_abort_handler = virtscsi_abort,
> .eh_device_reset_handler = virtscsi_device_reset,
> --
> 2.21.0
>

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming Lei