scsi: virtio_scsi: implement request batching

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>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/virtio_scsi.c

@@ -369,14 +369,7 @@ 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)
 {
@@ -421,17 +414,39 @@ 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);
@@ -496,6 +511,7 @@ 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;
@@ -525,7 +541,8 @@ 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);
@@ -543,8 +560,8 @@ static int virtscsi_tmf(struct virtio_scsi *vscsi, struct virtio_scsi_cmd *cmd)
 	int ret = FAILED;
 
 	cmd->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);
@@ -658,6 +675,13 @@ 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
@@ -675,6 +699,7 @@ 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,