virtio-scsi: Implement change_queue_depth for virtscsi targets

change_queue_depth allows changing per-target queue depth via sysfs.

It also allows the SCSI midlayer to ramp down the number of concurrent
inflight requests in response to a SCSI BUSY status response and allows
the midlayer to ramp the count back up to the device maximum when the
BUSY condition has resolved.

Signed-off-by: Venkatesh Srinivas <venkateshs@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

1 files changed, 33 insertions, 0 deletions

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index cdce502c3c46..eee1bc0b506e 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -27,6 +27,7 @@
 #include <scsi/scsi_host.h>
 #include <scsi/scsi_device.h>
 #include <scsi/scsi_cmnd.h>
+#include <scsi/scsi_tcq.h>
 #include <linux/seqlock.h>
 
 #define VIRTIO_SCSI_MEMPOOL_SZ 64
@@ -654,6 +655,36 @@ static int virtscsi_device_reset(struct scsi_cmnd *sc)
         return virtscsi_tmf(vscsi, cmd);
 }
 
+/**
+ * virtscsi_change_queue_depth() - Change a virtscsi target's queue depth
+ * @sdev:       Virtscsi target whose queue depth to change
+ * @qdepth:     New queue depth
+ * @reason:     Reason for the queue depth change.
+ */
+static int virtscsi_change_queue_depth(struct scsi_device *sdev,
+                                       int qdepth,
+                                       int reason)
+{
+        struct Scsi_Host *shost = sdev->host;
+        int max_depth = shost->cmd_per_lun;
+
+        switch (reason) {
+        case SCSI_QDEPTH_QFULL: /* Drop qdepth in response to BUSY state */
+                scsi_track_queue_full(sdev, qdepth);
+                break;
+        case SCSI_QDEPTH_RAMP_UP: /* Raise qdepth after BUSY state resolved */
+        case SCSI_QDEPTH_DEFAULT: /* Manual change via sysfs */
+                scsi_adjust_queue_depth(sdev,
+                                        scsi_get_tag_type(sdev),
+                                        min(max_depth, qdepth));
+                break;
+        default:
+                return -EOPNOTSUPP;
+        }
+
+        return sdev->queue_depth;
+}
+
 static int virtscsi_abort(struct scsi_cmnd *sc)
 {
         struct virtio_scsi *vscsi = shost_priv(sc->device->host);
@@ -709,6 +740,7 @@ static struct scsi_host_template virtscsi_host_template_single = {
         .this_id = -1,
         .cmd_size = sizeof(struct virtio_scsi_cmd),
         .queuecommand = virtscsi_queuecommand_single,
+        .change_queue_depth = virtscsi_change_queue_depth,
         .eh_abort_handler = virtscsi_abort,
         .eh_device_reset_handler = virtscsi_device_reset,
 
@@ -726,6 +758,7 @@ static struct scsi_host_template virtscsi_host_template_multi = {
         .this_id = -1,
         .cmd_size = sizeof(struct virtio_scsi_cmd),
         .queuecommand = virtscsi_queuecommand_multi,
+        .change_queue_depth = virtscsi_change_queue_depth,
         .eh_abort_handler = virtscsi_abort,
         .eh_device_reset_handler = virtscsi_device_reset,