net: virtio_net: notifications coalescing support

New VirtIO network feature: VIRTIO_NET_F_NOTF_COAL.

Control a Virtio network device notifications coalescing parameters
using the control virtqueue.

A device that supports this fetature can receive
VIRTIO_NET_CTRL_NOTF_COAL control commands.

- VIRTIO_NET_CTRL_NOTF_COAL_TX_SET:
  Ask the network device to change the following parameters:
  - tx_usecs: Maximum number of usecs to delay a TX notification.
  - tx_max_packets: Maximum number of packets to send before a
    TX notification.

- VIRTIO_NET_CTRL_NOTF_COAL_RX_SET:
  Ask the network device to change the following parameters:
  - rx_usecs: Maximum number of usecs to delay a RX notification.
  - rx_max_packets: Maximum number of packets to receive before a
    RX notification.

VirtIO spec. patch:
https://lists.oasis-open.org/archives/virtio-comment/202206/msg00100.html

Signed-off-by: Alvaro Karsz <alvaro.karsz@solid-run.com>
Message-Id: <20220718091102.498774-1-alvaro.karsz@solid-run.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/net/virtio_net.c

@@ -270,6 +270,12 @@ struct virtnet_info {
 	u8 duplex;
 	u32 speed;
 
+	/* Interrupt coalescing settings */
+	u32 tx_usecs;
+	u32 rx_usecs;
+	u32 tx_max_packets;
+	u32 rx_max_packets;
+
 	unsigned long guest_offloads;
 	unsigned long guest_offloads_capable;
 
@@ -2737,27 +2743,89 @@ static int virtnet_get_link_ksettings(struct net_device *dev,
 	return 0;
 }
 
+static int virtnet_send_notf_coal_cmds(struct virtnet_info *vi,
+				       struct ethtool_coalesce *ec)
+{
+	struct scatterlist sgs_tx, sgs_rx;
+	struct virtio_net_ctrl_coal_tx coal_tx;
+	struct virtio_net_ctrl_coal_rx coal_rx;
+
+	coal_tx.tx_usecs = cpu_to_le32(ec->tx_coalesce_usecs);
+	coal_tx.tx_max_packets = cpu_to_le32(ec->tx_max_coalesced_frames);
+	sg_init_one(&sgs_tx, &coal_tx, sizeof(coal_tx));
+
+	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_NOTF_COAL,
+				  VIRTIO_NET_CTRL_NOTF_COAL_TX_SET,
+				  &sgs_tx))
+		return -EINVAL;
+
+	/* Save parameters */
+	vi->tx_usecs = ec->tx_coalesce_usecs;
+	vi->tx_max_packets = ec->tx_max_coalesced_frames;
+
+	coal_rx.rx_usecs = cpu_to_le32(ec->rx_coalesce_usecs);
+	coal_rx.rx_max_packets = cpu_to_le32(ec->rx_max_coalesced_frames);
+	sg_init_one(&sgs_rx, &coal_rx, sizeof(coal_rx));
+
+	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_NOTF_COAL,
+				  VIRTIO_NET_CTRL_NOTF_COAL_RX_SET,
+				  &sgs_rx))
+		return -EINVAL;
+
+	/* Save parameters */
+	vi->rx_usecs = ec->rx_coalesce_usecs;
+	vi->rx_max_packets = ec->rx_max_coalesced_frames;
+
+	return 0;
+}
+
+static int virtnet_coal_params_supported(struct ethtool_coalesce *ec)
+{
+	/* usecs coalescing is supported only if VIRTIO_NET_F_NOTF_COAL
+	 * feature is negotiated.
+	 */
+	if (ec->rx_coalesce_usecs || ec->tx_coalesce_usecs)
+		return -EOPNOTSUPP;
+
+	if (ec->tx_max_coalesced_frames > 1 ||
+	    ec->rx_max_coalesced_frames != 1)
+		return -EINVAL;
+
+	return 0;
+}
+
 static int virtnet_set_coalesce(struct net_device *dev,
 				struct ethtool_coalesce *ec,
 				struct kernel_ethtool_coalesce *kernel_coal,
 				struct netlink_ext_ack *extack)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
-	int i, napi_weight;
+	int ret, i, napi_weight;
-
+	bool update_napi = false;
-	if (ec->tx_max_coalesced_frames > 1 ||
-	    ec->rx_max_coalesced_frames != 1)
-		return -EINVAL;
 
+	/* Can't change NAPI weight if the link is up */
 	napi_weight = ec->tx_max_coalesced_frames ? NAPI_POLL_WEIGHT : 0;
 	if (napi_weight ^ vi->sq[0].napi.weight) {
 		if (dev->flags & IFF_UP)
 			return -EBUSY;
+		else
+			update_napi = true;
+	}
+
+	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL))
+		ret = virtnet_send_notf_coal_cmds(vi, ec);
+	else
+		ret = virtnet_coal_params_supported(ec);
+
+	if (ret)
+		return ret;
+
+	if (update_napi) {
 		for (i = 0; i < vi->max_queue_pairs; i++)
 			vi->sq[i].napi.weight = napi_weight;
 	}
 
-	return 0;
+	return ret;
 }
 
 static int virtnet_get_coalesce(struct net_device *dev,
@@ -2765,16 +2833,19 @@ static int virtnet_get_coalesce(struct net_device *dev,
 				struct kernel_ethtool_coalesce *kernel_coal,
 				struct netlink_ext_ack *extack)
 {
-	struct ethtool_coalesce ec_default = {
-		.cmd = ETHTOOL_GCOALESCE,
-		.rx_max_coalesced_frames = 1,
-	};
 	struct virtnet_info *vi = netdev_priv(dev);
 
-	memcpy(ec, &ec_default, sizeof(ec_default));
+	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL)) {
+		ec->rx_coalesce_usecs = vi->rx_usecs;
+		ec->tx_coalesce_usecs = vi->tx_usecs;
+		ec->tx_max_coalesced_frames = vi->tx_max_packets;
+		ec->rx_max_coalesced_frames = vi->rx_max_packets;
+	} else {
+		ec->rx_max_coalesced_frames = 1;
 
 		if (vi->sq[0].napi.weight)
 			ec->tx_max_coalesced_frames = 1;
+	}
 
 	return 0;
 }
@@ -2893,7 +2964,8 @@ static int virtnet_set_rxnfc(struct net_device *dev, struct ethtool_rxnfc *info)
 }
 
 static const struct ethtool_ops virtnet_ethtool_ops = {
-	.supported_coalesce_params = ETHTOOL_COALESCE_MAX_FRAMES,
+	.supported_coalesce_params = ETHTOOL_COALESCE_MAX_FRAMES |
+		ETHTOOL_COALESCE_USECS,
 	.get_drvinfo = virtnet_get_drvinfo,
 	.get_link = ethtool_op_get_link,
 	.get_ringparam = virtnet_get_ringparam,
@@ -3606,6 +3678,8 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
 	     VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_RSS,
 			     "VIRTIO_NET_F_CTRL_VQ") ||
 	     VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_HASH_REPORT,
+			     "VIRTIO_NET_F_CTRL_VQ") ||
+	     VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_NOTF_COAL,
 			     "VIRTIO_NET_F_CTRL_VQ"))) {
 		return false;
 	}
@@ -3742,6 +3816,13 @@ static int virtnet_probe(struct virtio_device *vdev)
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
 		vi->mergeable_rx_bufs = true;
 
+	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_NOTF_COAL)) {
+		vi->rx_usecs = 0;
+		vi->tx_usecs = 0;
+		vi->tx_max_packets = 0;
+		vi->rx_max_packets = 0;
+	}
+
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_HASH_REPORT))
 		vi->has_rss_hash_report = true;
 
@@ -3977,7 +4058,7 @@ static struct virtio_device_id id_table[] = {
 	VIRTIO_NET_F_CTRL_MAC_ADDR, \
 	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \
 	VIRTIO_NET_F_SPEED_DUPLEX, VIRTIO_NET_F_STANDBY, \
-	VIRTIO_NET_F_RSS, VIRTIO_NET_F_HASH_REPORT
+	VIRTIO_NET_F_RSS, VIRTIO_NET_F_HASH_REPORT, VIRTIO_NET_F_NOTF_COAL
 
 static unsigned int features[] = {
 	VIRTNET_FEATURES,

include/uapi/linux/virtio_net.h

@@ -56,7 +56,7 @@
 #define VIRTIO_NET_F_MQ	22	/* Device supports Receive Flow
 					 * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
-
+#define VIRTIO_NET_F_NOTF_COAL	53	/* Guest can handle notifications coalescing */
 #define VIRTIO_NET_F_HASH_REPORT  57	/* Supports hash report */
 #define VIRTIO_NET_F_RSS	  60	/* Supports RSS RX steering */
 #define VIRTIO_NET_F_RSC_EXT	  61	/* extended coalescing info */
@@ -355,4 +355,36 @@ struct virtio_net_hash_config {
 #define VIRTIO_NET_CTRL_GUEST_OFFLOADS   5
 #define VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET        0
 
+/*
+ * Control notifications coalescing.
+ *
+ * Request the device to change the notifications coalescing parameters.
+ *
+ * Available with the VIRTIO_NET_F_NOTF_COAL feature bit.
+ */
+#define VIRTIO_NET_CTRL_NOTF_COAL		6
+/*
+ * Set the tx-usecs/tx-max-packets patameters.
+ * tx-usecs - Maximum number of usecs to delay a TX notification.
+ * tx-max-packets - Maximum number of packets to send before a TX notification.
+ */
+struct virtio_net_ctrl_coal_tx {
+	__le32 tx_max_packets;
+	__le32 tx_usecs;
+};
+
+#define VIRTIO_NET_CTRL_NOTF_COAL_TX_SET		0
+
+/*
+ * Set the rx-usecs/rx-max-packets patameters.
+ * rx-usecs - Maximum number of usecs to delay a RX notification.
+ * rx-max-frames - Maximum number of packets to receive before a RX notification.
+ */
+struct virtio_net_ctrl_coal_rx {
+	__le32 rx_max_packets;
+	__le32 rx_usecs;
+};
+
+#define VIRTIO_NET_CTRL_NOTF_COAL_RX_SET		1
+
 #endif /* _UAPI_LINUX_VIRTIO_NET_H */