[Qemu-devel] [PATCH] virtio-net: Make virtio queue sizes configurable

[Patrik Hermansson <phermansson@gmail.com>]

This patch adds the option to specify virtio queue sizes. Currently the
queue sizes is hard coded to 256, which might not be suitable for all types
of applications. This patch makes it possible to specify the queue size between
256 to 1024.

The minimum value is chosen based on the current sizes of the virtio
queues. The maximum queue size is based upon VIRTQUEUE_SIZE_MAX.
---
 hw/net/virtio-net.c            | 31 ++++++++++++++++++++++++++++---
 include/hw/virtio/virtio-net.h |  8 +++++++-
 2 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index a877614..c4fcb39 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1326,20 +1326,40 @@ static void virtio_net_tx_bh(void *opaque)
     }
 }
 
+static void virtio_net_validate_queue_limit(uint16_t *queue_size)
+{
+    if (*queue_size > VIRTIO_QUEUE_SIZE_MAX) {
+        error_report("queue-size: %d, exceeds maximum allowed queue-size(%d),"
+                     "queue-size set to %d", *queue_size, VIRTIO_QUEUE_SIZE_MAX,
+                      VIRTIO_QUEUE_SIZE_MAX);
+        *queue_size = VIRTIO_QUEUE_SIZE_MAX;
+    } else if (*queue_size < VIRTIO_QUEUE_SIZE_MIN) {
+        error_report("queue-size: %d, below minimum allowed queue-size(%d),"
+                     "queue-size set to %d", *queue_size, VIRTIO_QUEUE_SIZE_MIN,
+                      VIRTIO_QUEUE_SIZE_MIN);
+        *queue_size = VIRTIO_QUEUE_SIZE_MIN;
+    }
+}
+
 static void virtio_net_add_queue(VirtIONet *n, int index)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(n);
 
-    n->vqs[index].rx_vq = virtio_add_queue(vdev, 256, virtio_net_handle_rx);
+    virtio_net_validate_queue_limit(&n->net_conf.rx_virtqueue_sz);
+    virtio_net_validate_queue_limit(&n->net_conf.tx_virtqueue_sz);
+    n->vqs[index].rx_vq = virtio_add_queue(vdev, n->net_conf.rx_virtqueue_sz,
+                                           virtio_net_handle_rx);
     if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
         n->vqs[index].tx_vq =
-            virtio_add_queue(vdev, 256, virtio_net_handle_tx_timer);
+            virtio_add_queue(vdev, n->net_conf.tx_virtqueue_sz,
+                             virtio_net_handle_tx_timer);
         n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
                                               virtio_net_tx_timer,
                                               &n->vqs[index]);
     } else {
         n->vqs[index].tx_vq =
-            virtio_add_queue(vdev, 256, virtio_net_handle_tx_bh);
+            virtio_add_queue(vdev, n->net_conf.tx_virtqueue_sz,
+                             virtio_net_handle_tx_bh);
         n->vqs[index].tx_bh = qemu_bh_new(virtio_net_tx_bh, &n->vqs[index]);
     }
 
@@ -1826,6 +1846,11 @@ static Property virtio_net_properties[] = {
     DEFINE_PROP_UINT32("x-txtimer", VirtIONet, net_conf.txtimer,
                        TX_TIMER_INTERVAL),
     DEFINE_PROP_INT32("x-txburst", VirtIONet, net_conf.txburst, TX_BURST),
+    DEFINE_PROP_UINT16("rx_virtqueue_sz", VirtIONet, net_conf.rx_virtqueue_sz,
+                       RX_VIRTQUEUE_SIZE),
+    DEFINE_PROP_UINT16("tx_virtqueue_sz", VirtIONet, net_conf.tx_virtqueue_sz,
+                       TX_VIRTQUEUE_SIZE),
+
     DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx),
     DEFINE_PROP_END_OF_LIST(),
 };
diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
index f3cc25f..dbcabbf 100644
--- a/include/hw/virtio/virtio-net.h
+++ b/include/hw/virtio/virtio-net.h
@@ -28,13 +28,19 @@
  * ensures fairness in the io path.  256 conveniently matches the
  * length of the TX queue and shows a good balance of performance
  * and latency. */
-#define TX_BURST 256
+#define VIRTIO_QUEUE_SIZE_MIN 256
+#define VIRTIO_QUEUE_SIZE_MAX VIRTQUEUE_MAX_SIZE
+#define RX_VIRTQUEUE_SIZE VIRTIO_QUEUE_SIZE_MIN
+#define TX_VIRTQUEUE_SIZE VIRTIO_QUEUE_SIZE_MIN
+#define TX_BURST TX_VIRTQUEUE_SIZE
 
 typedef struct virtio_net_conf
 {
     uint32_t txtimer;
     int32_t txburst;
     char *tx;
+    uint16_t rx_virtqueue_sz;
+    uint16_t tx_virtqueue_sz;
 } virtio_net_conf;
 
 /* Maximum packet size we can receive from tap device: header + 64k */
-- 
1.9.1