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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 9 Feb 2021 04:42:44 -0500

On Mon, Feb 08, 2021 at 01:55:57PM -0500, Willem de Bruijn wrote:
> From: Willem de Bruijn <[email-masked]>
> 
> 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.

If you do something like this, please do it in the validate
callback and clear the features you aren't using.

> 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 <[email-masked]>
> ---
>  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