virtio-blk: make queue size configurable

Depending on the configuration, it can be beneficial to adjust the virtio-blk
queue size to something other than the current default of 128. Add a new
property to make the queue size configurable.

Signed-off-by: Mark Kanda <mark.kanda@oracle.com>
Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Ameya More <ameya.more@oracle.com>
Message-id: 52e6d742811f10dbd16e996e86cf375b9577c187.1513005190.git.mark.kanda@oracle.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

hw/block/virtio-blk.c

@@ -928,6 +928,13 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
         error_setg(errp, "num-queues property must be larger than 0");
         return;
     }
+    if (!is_power_of_2(conf->queue_size) ||
+        conf->queue_size > VIRTQUEUE_MAX_SIZE) {
+        error_setg(errp, "invalid queue-size property (%" PRIu16 "), "
+                   "must be a power of 2 (max %d)",
+                   conf->queue_size, VIRTQUEUE_MAX_SIZE);
+        return;
+    }
 
     blkconf_serial(&conf->conf, &conf->serial);
     if (!blkconf_apply_backend_options(&conf->conf,
@@ -950,7 +957,7 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
     s->sector_mask = (s->conf.conf.logical_block_size / BDRV_SECTOR_SIZE) - 1;
 
     for (i = 0; i < conf->num_queues; i++) {
-        virtio_add_queue(vdev, 128, virtio_blk_handle_output);
+        virtio_add_queue(vdev, conf->queue_size, virtio_blk_handle_output);
     }
     virtio_blk_data_plane_create(vdev, conf, &s->dataplane, &err);
     if (err != NULL) {
@@ -1009,6 +1016,7 @@ static Property virtio_blk_properties[] = {
     DEFINE_PROP_BIT("request-merging", VirtIOBlock, conf.request_merging, 0,
                     true),
     DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1),
+    DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128),
     DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
                      IOThread *),
     DEFINE_PROP_END_OF_LIST(),

include/hw/virtio/virtio-blk.h

@@ -39,6 +39,7 @@ struct VirtIOBlkConf
     uint32_t config_wce;
     uint32_t request_merging;
     uint16_t num_queues;
+    uint16_t queue_size;
 };
 
 struct VirtIOBlockDataPlane;