[dpdk-dev] [PATCH v3 1/7] net/virtio: add Rx free threshold setting

[Marvin Liu <yong.liu@intel.com>]

Introduce free threshold setting in Rx queue, default value of it is 32.
Limiated threshold size to multiple of four as only vectorized packed Rx
function will utilize it. Virtio driver will rearm Rx queue when more
than rx_free_thresh descs were dequeued.

Signed-off-by: Marvin Liu <yong.liu@intel.com>

diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
index 752faa0f6..3a2dbc2e0 100644
--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -936,6 +936,7 @@ virtio_dev_rx_queue_setup(struct rte_eth_dev *dev,
 	struct virtio_hw *hw = dev->data->dev_private;
 	struct virtqueue *vq = hw->vqs[vtpci_queue_idx];
 	struct virtnet_rx *rxvq;
+	uint16_t rx_free_thresh;
 
 	PMD_INIT_FUNC_TRACE();
 
@@ -944,6 +945,28 @@ virtio_dev_rx_queue_setup(struct rte_eth_dev *dev,
 		return -EINVAL;
 	}
 
+	rx_free_thresh = rx_conf->rx_free_thresh;
+	if (rx_free_thresh == 0)
+		rx_free_thresh =
+			RTE_MIN(vq->vq_nentries / 4, DEFAULT_RX_FREE_THRESH);
+
+	if (rx_free_thresh & 0x3) {
+		RTE_LOG(ERR, PMD, "rx_free_thresh must be multiples of four."
+			" (rx_free_thresh=%u port=%u queue=%u)\n",
+			rx_free_thresh, dev->data->port_id, queue_idx);
+		return -EINVAL;
+	}
+
+	if (rx_free_thresh >= vq->vq_nentries) {
+		RTE_LOG(ERR, PMD, "rx_free_thresh must be less than the "
+			"number of RX entries (%u)."
+			" (rx_free_thresh=%u port=%u queue=%u)\n",
+			vq->vq_nentries,
+			rx_free_thresh, dev->data->port_id, queue_idx);
+		return -EINVAL;
+	}
+	vq->vq_free_thresh = rx_free_thresh;
+
 	if (nb_desc == 0 || nb_desc > vq->vq_nentries)
 		nb_desc = vq->vq_nentries;
 	vq->vq_free_cnt = RTE_MIN(vq->vq_free_cnt, nb_desc);
diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
index 58ad7309a..6301c56b2 100644
--- a/drivers/net/virtio/virtqueue.h
+++ b/drivers/net/virtio/virtqueue.h
@@ -18,6 +18,8 @@
 
 struct rte_mbuf;
 
+#define DEFAULT_RX_FREE_THRESH 32
+
 /*
  * Per virtio_ring.h in Linux.
  *     For virtio_pci on SMP, we don't need to order with respect to MMIO
-- 
2.17.1