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Willem de Bruijn

2021-Feb-08 18:55 UTC

[PATCH RFC v2 3/4] virtio-net: support transmit timestamp

From: Willem de Bruijn <willemb at google.com>

Add optional PTP hardware tx timestamp offload for virtio-net.

Accurate RTT measurement requires timestamps close to the wire.
Introduce virtio feature VIRTIO_NET_F_TX_TSTAMP, the transmit
equivalent to VIRTIO_NET_F_RX_TSTAMP.

The driver sets VIRTIO_NET_HDR_F_TSTAMP to request a timestamp
returned on completion. If the feature is negotiated, the device
either places the timestamp or clears the feature bit.

The timestamp straddles (virtual) hardware domains. Like PTP, use
international atomic time (CLOCK_TAI) as global clock base. The driver
must sync with the device, e.g., through kvm-clock.

Modify can_push to ensure that on tx completion the header, and thus
timestamp, is in a predicatable location at skb_vnet_hdr.

RFC: this implementation relies on the device writing to the buffer.
That breaks DMA_TO_DEVICE semantics. For now, disable when DMA is on.
The virtio changes should be a separate patch at the least.

Tested: modified txtimestamp.c to with h/w timestamping:
  -       sock_opt = SOF_TIMESTAMPING_SOFTWARE |
  +       sock_opt = SOF_TIMESTAMPING_RAW_HARDWARE |
  + do_test(family, SOF_TIMESTAMPING_TX_HARDWARE);

Signed-off-by: Willem de Bruijn <willemb at google.com>
---
 drivers/net/virtio_net.c        | 61 ++++++++++++++++++++++++++++-----
 drivers/virtio/virtio_ring.c    |  3 +-
 include/linux/virtio.h          |  1 +
 include/uapi/linux/virtio_net.h |  1 +
 4 files changed, 56 insertions(+), 10 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ac44c5efa0bc..fc8ecd3a333a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -210,6 +210,12 @@ struct virtnet_info {
 	/* Device will pass rx timestamp. Requires has_rx_tstamp */
 	bool enable_rx_tstamp;
 
+	/* Device can pass CLOCK_TAI transmit time to the driver */
+	bool has_tx_tstamp;
+
+	/* Device will pass tx timestamp. Requires has_tx_tstamp */
+	bool enable_tx_tstamp;
+
 	/* Has control virtqueue */
 	bool has_cvq;
 
@@ -1401,6 +1407,20 @@ static int virtnet_receive(struct receive_queue *rq, int
budget,
 	return stats.packets;
 }
 
+static void virtnet_record_tx_tstamp(const struct send_queue *sq,
+				     struct sk_buff *skb)
+{
+	const struct virtio_net_hdr_hash_ts *h = skb_vnet_hdr_ht(skb);
+	const struct virtnet_info *vi = sq->vq->vdev->priv;
+	struct skb_shared_hwtstamps ts;
+
+	if (h->hdr.flags & VIRTIO_NET_HDR_F_TSTAMP &&
+	    vi->enable_tx_tstamp) {
+		ts.hwtstamp = ns_to_ktime(le64_to_cpu(h->tstamp));
+		skb_tstamp_tx(skb, &ts);
+	}
+}
+
 static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
 {
 	unsigned int len;
@@ -1412,6 +1432,7 @@ static void free_old_xmit_skbs(struct send_queue *sq, bool
in_napi)
 		if (likely(!is_xdp_frame(ptr))) {
 			struct sk_buff *skb = ptr;
 
+			virtnet_record_tx_tstamp(sq, skb);
 			pr_debug("Sent skb %p\n", skb);
 
 			bytes += skb->len;
@@ -1558,7 +1579,7 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff
*skb)
 	struct virtio_net_hdr_mrg_rxbuf *hdr;
 	const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
 	struct virtnet_info *vi = sq->vq->vdev->priv;
-	struct virtio_net_hdr_v1_hash *ht;
+	struct virtio_net_hdr_hash_ts *ht;
 	int num_sg;
 	unsigned hdr_len = vi->hdr_len;
 	bool can_push;
@@ -1567,7 +1588,8 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff
*skb)
 
 	can_push = vi->any_header_sg &&
 		!((unsigned long)skb->data & (__alignof__(*hdr) - 1)) &&
-		!skb_header_cloned(skb) && skb_headroom(skb) >= hdr_len;
+		!skb_header_cloned(skb) && skb_headroom(skb) >= hdr_len &&
+		!vi->enable_tx_tstamp;
 	/* Even if we can, don't push here yet as this would skew
 	 * csum_start offset below. */
 	if (can_push)
@@ -1588,10 +1610,12 @@ static int xmit_skb(struct send_queue *sq, struct
sk_buff *skb)
 		u16 report = skb->l4_hash ? VIRTIO_NET_HASH_REPORT_L4 :
 					    VIRTIO_NET_HASH_REPORT_OTHER;
 
-		ht->hash_value = cpu_to_le32(skb->hash);
-		ht->hash_report = cpu_to_le16(report);
-		ht->hash_state = cpu_to_le16(VIRTIO_NET_HASH_STATE_DEFAULT);
+		ht->hash.value = cpu_to_le32(skb->hash);
+		ht->hash.report = cpu_to_le16(report);
+		ht->hash.flow_state = cpu_to_le16(VIRTIO_NET_HASH_STATE_DEFAULT);
 	}
+	if (vi->enable_tx_tstamp && skb_shinfo(skb)->tx_flags &
SKBTX_HW_TSTAMP)
+		ht->hdr.flags |= VIRTIO_NET_HDR_F_TSTAMP;
 
 	sg_init_table(sq->sg, skb_shinfo(skb)->nr_frags + (can_push ? 1 : 2));
 	if (can_push) {
@@ -2307,7 +2331,13 @@ static int virtnet_get_ts_info(struct net_device *dev,
 		info->rx_filters = HWTSTAMP_FILTER_NONE;
 	}
 
-	info->tx_types = HWTSTAMP_TX_OFF;
+	if (vi->has_tx_tstamp) {
+		info->so_timestamping |= SOF_TIMESTAMPING_TX_HARDWARE |
+					 SOF_TIMESTAMPING_RAW_HARDWARE;
+		info->tx_types = HWTSTAMP_TX_ON;
+	} else {
+		info->tx_types = HWTSTAMP_TX_OFF;
+	}
 
 	return 0;
 }
@@ -2616,7 +2646,8 @@ static int virtnet_ioctl_set_hwtstamp(struct net_device
*dev, struct ifreq *ifr)
 		return -EFAULT;
 	if (tsconf.flags)
 		return -EINVAL;
-	if (tsconf.tx_type != HWTSTAMP_TX_OFF)
+	if (tsconf.tx_type != HWTSTAMP_TX_OFF &&
+	    tsconf.tx_type != HWTSTAMP_TX_ON)
 		return -ERANGE;
 	if (tsconf.rx_filter != HWTSTAMP_FILTER_NONE &&
 	    tsconf.rx_filter != HWTSTAMP_FILTER_ALL)
@@ -2627,6 +2658,11 @@ static int virtnet_ioctl_set_hwtstamp(struct net_device
*dev, struct ifreq *ifr)
 	else
 		vi->enable_rx_tstamp = tsconf.rx_filter == HWTSTAMP_FILTER_ALL;
 
+	if (!vi->has_tx_tstamp)
+		tsconf.tx_type = HWTSTAMP_TX_OFF;
+	else
+		vi->enable_tx_tstamp = tsconf.tx_type == HWTSTAMP_TX_ON;
+
 	if (copy_to_user(ifr->ifr_data, &tsconf, sizeof(tsconf)))
 		return -EFAULT;
 
@@ -2641,7 +2677,8 @@ static int virtnet_ioctl_get_hwtstamp(struct net_device
*dev, struct ifreq *ifr)
 	tsconf.flags = 0;
 	tsconf.rx_filter = vi->enable_rx_tstamp ? HWTSTAMP_FILTER_ALL :
 						  HWTSTAMP_FILTER_NONE;
-	tsconf.tx_type = HWTSTAMP_TX_OFF;
+	tsconf.tx_type = vi->enable_tx_tstamp ? HWTSTAMP_TX_ON :
+						HWTSTAMP_TX_OFF;
 
 	if (copy_to_user(ifr->ifr_data, &tsconf, sizeof(tsconf)))
 		return -EFAULT;
@@ -3178,6 +3215,12 @@ static int virtnet_probe(struct virtio_device *vdev)
 		vi->hdr_len = sizeof(struct virtio_net_hdr_hash_ts);
 	}
 
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_TX_TSTAMP) &&
+	    !vring_use_dma_api(vdev)) {
+		vi->has_tx_tstamp = true;
+		vi->hdr_len = sizeof(struct virtio_net_hdr_hash_ts);
+	}
+
 	if (virtio_has_feature(vdev, VIRTIO_F_ANY_LAYOUT) ||
 	    virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
 		vi->any_header_sg = true;
@@ -3369,7 +3412,7 @@ 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_TX_HASH, VIRTIO_NET_F_RX_TSTAMP
+	VIRTIO_NET_F_TX_HASH, VIRTIO_NET_F_RX_TSTAMP, VIRTIO_NET_F_TX_TSTAMP
 
 static unsigned int features[] = {
 	VIRTNET_FEATURES,
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 71e16b53e9c1..cf5d5d1f9b14 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -238,7 +238,7 @@ static inline bool virtqueue_use_indirect(struct virtqueue
*_vq,
  * unconditionally on data path.
  */
 
-static bool vring_use_dma_api(struct virtio_device *vdev)
+bool vring_use_dma_api(struct virtio_device *vdev)
 {
 	if (!virtio_has_dma_quirk(vdev))
 		return true;
@@ -257,6 +257,7 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
 
 	return false;
 }
+EXPORT_SYMBOL_GPL(vring_use_dma_api);
 
 size_t virtio_max_dma_size(struct virtio_device *vdev)
 {
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 55ea329fe72a..5289e2812e95 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -140,6 +140,7 @@ int virtio_device_freeze(struct virtio_device *dev);
 int virtio_device_restore(struct virtio_device *dev);
 #endif
 
+bool vring_use_dma_api(struct virtio_device *vdev);
 size_t virtio_max_dma_size(struct virtio_device *vdev);
 
 #define virtio_device_for_each_vq(vdev, vq) \
diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index a5c84410cf92..b5d6f0c6cead 100644
--- a/include/uapi/linux/virtio_net.h
+++ b/include/uapi/linux/virtio_net.h
@@ -57,6 +57,7 @@
 					 * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
 
+#define VIRTIO_NET_F_TX_TSTAMP	  54	/* Device sends TAI transmit time */
 #define VIRTIO_NET_F_RX_TSTAMP	  55	/* Device sends TAI receive time */
 #define VIRTIO_NET_F_TX_HASH	  56	/* Driver sends hash report */
 #define VIRTIO_NET_F_HASH_REPORT  57	/* Supports hash report */
-- 
2.30.0.478.g8a0d178c01-goog

Jason Wang

2021-Feb-09 05:45 UTC

head link

[PATCH RFC v2 3/4] virtio-net: support transmit timestamp

On 2021/2/9 ??2:55, Willem de Bruijn wrote:> From: Willem de Bruijn <willemb at google.com>
>
> Add optional PTP hardware tx timestamp offload for virtio-net.
>
> Accurate RTT measurement requires timestamps close to the wire.
> Introduce virtio feature VIRTIO_NET_F_TX_TSTAMP, the transmit
> equivalent to VIRTIO_NET_F_RX_TSTAMP.
>
> The driver sets VIRTIO_NET_HDR_F_TSTAMP to request a timestamp
> returned on completion. If the feature is negotiated, the device
> either places the timestamp or clears the feature bit.
>
> The timestamp straddles (virtual) hardware domains. Like PTP, use
> international atomic time (CLOCK_TAI) as global clock base. The driver
> must sync with the device, e.g., through kvm-clock.
>
> Modify can_push to ensure that on tx completion the header, and thus
> timestamp, is in a predicatable location at skb_vnet_hdr.
>
> RFC: this implementation relies on the device writing to the buffer.
> That breaks DMA_TO_DEVICE semantics. For now, disable when DMA is on.
> The virtio changes should be a separate patch at the least.
>
> Tested: modified txtimestamp.c to with h/w timestamping:
>    -       sock_opt = SOF_TIMESTAMPING_SOFTWARE |
>    +       sock_opt = SOF_TIMESTAMPING_RAW_HARDWARE |
>    + do_test(family, SOF_TIMESTAMPING_TX_HARDWARE);
>
> Signed-off-by: Willem de Bruijn <willemb at google.com>
> ---
>   drivers/net/virtio_net.c        | 61 ++++++++++++++++++++++++++++-----
>   drivers/virtio/virtio_ring.c    |  3 +-
>   include/linux/virtio.h          |  1 +
>   include/uapi/linux/virtio_net.h |  1 +
>   4 files changed, 56 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ac44c5efa0bc..fc8ecd3a333a 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -210,6 +210,12 @@ struct virtnet_info {
>   	/* Device will pass rx timestamp. Requires has_rx_tstamp */
>   	bool enable_rx_tstamp;
>   
> +	/* Device can pass CLOCK_TAI transmit time to the driver */
> +	bool has_tx_tstamp;
> +
> +	/* Device will pass tx timestamp. Requires has_tx_tstamp */
> +	bool enable_tx_tstamp;
> +
>   	/* Has control virtqueue */
>   	bool has_cvq;
>   
> @@ -1401,6 +1407,20 @@ static int virtnet_receive(struct receive_queue *rq,
int budget,
>   	return stats.packets;
>   }
>   
> +static void virtnet_record_tx_tstamp(const struct send_queue *sq,
> +				     struct sk_buff *skb)
> +{
> +	const struct virtio_net_hdr_hash_ts *h = skb_vnet_hdr_ht(skb);
> +	const struct virtnet_info *vi = sq->vq->vdev->priv;
> +	struct skb_shared_hwtstamps ts;
> +
> +	if (h->hdr.flags & VIRTIO_NET_HDR_F_TSTAMP &&
> +	    vi->enable_tx_tstamp) {
> +		ts.hwtstamp = ns_to_ktime(le64_to_cpu(h->tstamp));
> +		skb_tstamp_tx(skb, &ts);

This probably won't work since the buffer is read-only from the device. 
(See virtqueue_add_outbuf()).

Another issue that I vaguely remember that the virtio spec forbids out 
buffer after in buffer.

> +	}
> +}
> +
>   static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
>   {
>   	unsigned int len;
> @@ -1412,6 +1432,7 @@ static void free_old_xmit_skbs(struct send_queue *sq,
bool in_napi)
>   		if (likely(!is_xdp_frame(ptr))) {
>   			struct sk_buff *skb = ptr;
>   
> +			virtnet_record_tx_tstamp(sq, skb);
>   			pr_debug("Sent skb %p\n", skb);
>   
>   			bytes += skb->len;
> @@ -1558,7 +1579,7 @@ static int xmit_skb(struct send_queue *sq, struct
sk_buff *skb)
>   	struct virtio_net_hdr_mrg_rxbuf *hdr;
>   	const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
>   	struct virtnet_info *vi = sq->vq->vdev->priv;
> -	struct virtio_net_hdr_v1_hash *ht;
> +	struct virtio_net_hdr_hash_ts *ht;
>   	int num_sg;
>   	unsigned hdr_len = vi->hdr_len;
>   	bool can_push;
> @@ -1567,7 +1588,8 @@ static int xmit_skb(struct send_queue *sq, struct
sk_buff *skb)
>   
>   	can_push = vi->any_header_sg &&
>   		!((unsigned long)skb->data & (__alignof__(*hdr) - 1)) &&
> -		!skb_header_cloned(skb) && skb_headroom(skb) >= hdr_len;
> +		!skb_header_cloned(skb) && skb_headroom(skb) >= hdr_len
&&
> +		!vi->enable_tx_tstamp;
>   	/* Even if we can, don't push here yet as this would skew
>   	 * csum_start offset below. */
>   	if (can_push)
> @@ -1588,10 +1610,12 @@ static int xmit_skb(struct send_queue *sq, struct
sk_buff *skb)
>   		u16 report = skb->l4_hash ? VIRTIO_NET_HASH_REPORT_L4 :
>   					    VIRTIO_NET_HASH_REPORT_OTHER;
>   
> -		ht->hash_value = cpu_to_le32(skb->hash);
> -		ht->hash_report = cpu_to_le16(report);
> -		ht->hash_state = cpu_to_le16(VIRTIO_NET_HASH_STATE_DEFAULT);
> +		ht->hash.value = cpu_to_le32(skb->hash);
> +		ht->hash.report = cpu_to_le16(report);
> +		ht->hash.flow_state = cpu_to_le16(VIRTIO_NET_HASH_STATE_DEFAULT);
>   	}
> +	if (vi->enable_tx_tstamp && skb_shinfo(skb)->tx_flags &
SKBTX_HW_TSTAMP)
> +		ht->hdr.flags |= VIRTIO_NET_HDR_F_TSTAMP;
>   
>   	sg_init_table(sq->sg, skb_shinfo(skb)->nr_frags + (can_push ? 1 :
2));
>   	if (can_push) {
> @@ -2307,7 +2331,13 @@ static int virtnet_get_ts_info(struct net_device
*dev,
>   		info->rx_filters = HWTSTAMP_FILTER_NONE;
>   	}
>   
> -	info->tx_types = HWTSTAMP_TX_OFF;
> +	if (vi->has_tx_tstamp) {
> +		info->so_timestamping |= SOF_TIMESTAMPING_TX_HARDWARE |
> +					 SOF_TIMESTAMPING_RAW_HARDWARE;
> +		info->tx_types = HWTSTAMP_TX_ON;
> +	} else {
> +		info->tx_types = HWTSTAMP_TX_OFF;
> +	}
>   
>   	return 0;
>   }
> @@ -2616,7 +2646,8 @@ static int virtnet_ioctl_set_hwtstamp(struct
net_device *dev, struct ifreq *ifr)
>   		return -EFAULT;
>   	if (tsconf.flags)
>   		return -EINVAL;
> -	if (tsconf.tx_type != HWTSTAMP_TX_OFF)
> +	if (tsconf.tx_type != HWTSTAMP_TX_OFF &&
> +	    tsconf.tx_type != HWTSTAMP_TX_ON)
>   		return -ERANGE;
>   	if (tsconf.rx_filter != HWTSTAMP_FILTER_NONE &&
>   	    tsconf.rx_filter != HWTSTAMP_FILTER_ALL)
> @@ -2627,6 +2658,11 @@ static int virtnet_ioctl_set_hwtstamp(struct
net_device *dev, struct ifreq *ifr)
>   	else
>   		vi->enable_rx_tstamp = tsconf.rx_filter == HWTSTAMP_FILTER_ALL;
>   
> +	if (!vi->has_tx_tstamp)
> +		tsconf.tx_type = HWTSTAMP_TX_OFF;
> +	else
> +		vi->enable_tx_tstamp = tsconf.tx_type == HWTSTAMP_TX_ON;
> +
>   	if (copy_to_user(ifr->ifr_data, &tsconf, sizeof(tsconf)))
>   		return -EFAULT;
>   
> @@ -2641,7 +2677,8 @@ static int virtnet_ioctl_get_hwtstamp(struct
net_device *dev, struct ifreq *ifr)
>   	tsconf.flags = 0;
>   	tsconf.rx_filter = vi->enable_rx_tstamp ? HWTSTAMP_FILTER_ALL :
>   						  HWTSTAMP_FILTER_NONE;
> -	tsconf.tx_type = HWTSTAMP_TX_OFF;
> +	tsconf.tx_type = vi->enable_tx_tstamp ? HWTSTAMP_TX_ON :
> +						HWTSTAMP_TX_OFF;
>   
>   	if (copy_to_user(ifr->ifr_data, &tsconf, sizeof(tsconf)))
>   		return -EFAULT;
> @@ -3178,6 +3215,12 @@ static int virtnet_probe(struct virtio_device *vdev)
>   		vi->hdr_len = sizeof(struct virtio_net_hdr_hash_ts);
>   	}
>   
> +	if (virtio_has_feature(vdev, VIRTIO_NET_F_TX_TSTAMP) &&
> +	    !vring_use_dma_api(vdev)) {
> +		vi->has_tx_tstamp = true;
> +		vi->hdr_len = sizeof(struct virtio_net_hdr_hash_ts);
> +	}
> +
>   	if (virtio_has_feature(vdev, VIRTIO_F_ANY_LAYOUT) ||
>   	    virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
>   		vi->any_header_sg = true;
> @@ -3369,7 +3412,7 @@ 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_TX_HASH, VIRTIO_NET_F_RX_TSTAMP
> +	VIRTIO_NET_F_TX_HASH, VIRTIO_NET_F_RX_TSTAMP, VIRTIO_NET_F_TX_TSTAMP
>   
>   static unsigned int features[] = {
>   	VIRTNET_FEATURES,
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 71e16b53e9c1..cf5d5d1f9b14 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -238,7 +238,7 @@ static inline bool virtqueue_use_indirect(struct
virtqueue *_vq,
>    * unconditionally on data path.
>    */
>   
> -static bool vring_use_dma_api(struct virtio_device *vdev)
> +bool vring_use_dma_api(struct virtio_device *vdev)
>   {
>   	if (!virtio_has_dma_quirk(vdev))
>   		return true;
> @@ -257,6 +257,7 @@ static bool vring_use_dma_api(struct virtio_device
*vdev)
>   
>   	return false;
>   }
> +EXPORT_SYMBOL_GPL(vring_use_dma_api);
>   
>   size_t virtio_max_dma_size(struct virtio_device *vdev)
>   {
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 55ea329fe72a..5289e2812e95 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -140,6 +140,7 @@ int virtio_device_freeze(struct virtio_device *dev);
>   int virtio_device_restore(struct virtio_device *dev);
>   #endif
>   
> +bool vring_use_dma_api(struct virtio_device *vdev);
>   size_t virtio_max_dma_size(struct virtio_device *vdev);
>   
>   #define virtio_device_for_each_vq(vdev, vq) \
> diff --git a/include/uapi/linux/virtio_net.h
b/include/uapi/linux/virtio_net.h
> index a5c84410cf92..b5d6f0c6cead 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -57,6 +57,7 @@
>   					 * Steering */
>   #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
>   
> +#define VIRTIO_NET_F_TX_TSTAMP	  54	/* Device sends TAI transmit time */
>   #define VIRTIO_NET_F_RX_TSTAMP	  55	/* Device sends TAI receive time */

I wonder how much value to split into two features.

Thanks

>   #define VIRTIO_NET_F_TX_HASH	  56	/* Driver sends hash report */
>   #define VIRTIO_NET_F_HASH_REPORT  57	/* Supports hash report */

Virtualization - Feb 2021 - [PATCH RFC v2 3/4] virtio-net: support transmit timestamp

[PATCH RFC v2 3/4] virtio-net: support transmit timestamp

[PATCH RFC v2 3/4] virtio-net: support transmit timestamp