[PATCH 2/2] virtio_scsi: implement request batching

[Paolo Bonzini]

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 <stefa...@redhat.com>
Signed-off-by: Paolo Bonzini <pbonz...@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