Subject: Re: [PATCH] net: virtio_net: support interrupt coalescing

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 12 May 2022 05:55:31 -0400

On Thu, May 12, 2022 at 11:35:23AM +0300, Alvaro Karsz wrote:
> Control a Virtio network device interrupt coalescing parameters
> using the control virtqueue.
> 
> New VirtIO network feature: VIRTIO_NET_F_INTR_COAL.
> 
> A device that supports this fetature can receive
> VIRTIO_NET_CTRL_INTR_COAL control commands.
> 
> * VIRTIO_NET_CTRL_INTR_COAL_USECS_SET:
> 	change the rx-usecs and tx-usecs parameters.
> 
> 	rx-usecs - Time to delay an RX interrupt after packet arrival in
> 		microseconds.
> 
> 	tx-usecs - Time to delay a TX interrupt after a sending a packet
> 		in microseconds.
> 
> * VIRTIO_NET_CTRL_INTR_COAL_FRAMES_SET:
> 	change the rx-max-frames and tx-max-frames parameters.
> 
> 	rx-max-frames: Number of packets to delay an RX interrupt after
> 		packet arrival.
> 
> 	tx-max-frames: Number of packets to delay a TX interrupt after
> 		sending a packet.
> 
> Signed-off-by: Alvaro Karsz <[email-masked]>

So first, please at least reserve the feature in the virtio spec.
Preferably add the specification as well.
Here's one way to do it:
https://github.com/oasis-tcs/virtio-spec#use-of-github-issues

> ---
>  drivers/net/virtio_net.c        | 108 ++++++++++++++++++++++++++++----
>  include/uapi/linux/virtio_net.h |  34 +++++++++-
>  2 files changed, 128 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index cbba9d2e8f3..4806c35ddd5 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -261,6 +261,12 @@ struct virtnet_info {
>  	u8 duplex;
>  	u32 speed;
> 
> +	/* Interrupt coalescing settings */
> +	u32 tx_usecs;
> +	u32 rx_usecs;
> +	u32 tx_frames_max;
> +	u32 rx_frames_max;
> +
>  	unsigned long guest_offloads;
>  	unsigned long guest_offloads_capable;
> 
> @@ -2594,19 +2600,75 @@ static int virtnet_set_coalesce(struct net_device *dev,
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	int i, napi_weight;
> +	struct scatterlist sgs_usecs, sgs_frames;
> +	struct virtio_net_ctrl_coal_frames c_frames;
> +	struct virtio_net_ctrl_coal_usec c_usecs;
> +	bool update_napi,
> +	intr_coal = virtio_has_feature(vi->vdev, VIRTIO_NET_F_INTR_COAL);
> +
> +	/* rx_coalesce_usecs/tx_coalesce_usecs are supported only
> +	 * if VIRTIO_NET_F_INTR_COAL feature is set.
> +	 */
> +	if (!intr_coal && (ec->rx_coalesce_usecs || ec->tx_coalesce_usecs))
> +		return -EOPNOTSUPP;
> +
> +	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_INTR_COAL)) {
> +		/* Send usec command */
> +		c_usecs.tx_usecs = ec->tx_coalesce_usecs;
> +		c_usecs.rx_usecs = ec->rx_coalesce_usecs;
> +		sg_init_one(&sgs_usecs, &c_usecs, sizeof(c_usecs));
> +
> +		if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_INTR_COAL,
> +					  VIRTIO_NET_CTRL_INTR_COAL_USECS_SET,
> +					  &sgs_usecs))
> +			return -EINVAL;
> +
> +		/* Save parameters */
> +		vi->tx_usecs = ec->tx_coalesce_usecs;
> +		vi->rx_usecs = ec->rx_coalesce_usecs;
> +
> +		/* Send frames command */
> +		c_frames.tx_frames_max = ec->tx_max_coalesced_frames;
> +		c_frames.rx_frames_max = ec->rx_max_coalesced_frames;
> +		sg_init_one(&sgs_frames, &c_frames, sizeof(c_frames));
> +
> +		if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_INTR_COAL,
> +					  VIRTIO_NET_CTRL_INTR_COAL_FRAMES_SET,
> +					  &sgs_frames))
> +			return -EINVAL;
> +
> +		/* Save parameters */
> +		vi->tx_frames_max = ec->tx_max_coalesced_frames;
> +		vi->rx_frames_max = ec->rx_max_coalesced_frames;

> +	}
> +
> +	/* Should we update NAPI? */
> +	update_napi = ec->tx_max_coalesced_frames <= 1 &&
> +			ec->rx_max_coalesced_frames == 1;
> 
> -	if (ec->tx_max_coalesced_frames > 1 ||
> -	    ec->rx_max_coalesced_frames != 1)
> +	/* If interrupt coalesing feature is not set, and we can't update NAPI, return an error */
> +	if (!intr_coal && !update_napi)
>  		return -EINVAL;
> 
> -	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;
> -		for (i = 0; i < vi->max_queue_pairs; i++)
> -			vi->sq[i].napi.weight = napi_weight;
> +	if (update_napi) {
> +		napi_weight = ec->tx_max_coalesced_frames ? NAPI_POLL_WEIGHT : 0;
> +		if (napi_weight ^ vi->sq[0].napi.weight) {
> +			if (dev->flags & IFF_UP) {
> +				/* If Interrupt coalescing feature is not set, return an error.
> +				 * Otherwise exit without changing the NAPI paremeters
> +				 */
> +				if (!intr_coal)
> +					return -EBUSY;
> +
> +				goto exit;
> +			}
> +
> +			for (i = 0; i < vi->max_queue_pairs; i++)
> +				vi->sq[i].napi.weight = napi_weight;
> +		}
>  	}
> 
> +exit:
>  	return 0;
>  }
> 
> @@ -2616,14 +2678,25 @@ static int virtnet_get_coalesce(struct net_device *dev,
>  				struct netlink_ext_ack *extack)
>  {
>  	struct ethtool_coalesce ec_default = {
> -		.cmd = ETHTOOL_GCOALESCE,
> -		.rx_max_coalesced_frames = 1,
> +		.cmd = ETHTOOL_GCOALESCE
>  	};
> +
>  	struct virtnet_info *vi = netdev_priv(dev);
> +	bool intr_coal = virtio_has_feature(vi->vdev, VIRTIO_NET_F_INTR_COAL);
> +
> +	/* Add Interrupt coalescing settings */
> +	if (intr_coal) {
> +		ec_default.rx_coalesce_usecs = vi->rx_usecs;
> +		ec_default.tx_coalesce_usecs = vi->tx_usecs;
> +		ec_default.tx_max_coalesced_frames = vi->tx_frames_max;
> +		ec_default.rx_max_coalesced_frames = vi->rx_frames_max;
> +	} else {
> +		ec_default.rx_max_coalesced_frames = 1;
> +	}
> 
>  	memcpy(ec, &ec_default, sizeof(ec_default));
> 
> -	if (vi->sq[0].napi.weight)
> +	if (!intr_coal && vi->sq[0].napi.weight)
>  		ec->tx_max_coalesced_frames = 1;
> 
>  	return 0;
> @@ -2743,7 +2816,7 @@ 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,
> @@ -3423,6 +3496,8 @@ 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_INTR_COAL,
>  			     "VIRTIO_NET_F_CTRL_VQ"))) {
>  		return false;
>  	}
> @@ -3558,6 +3633,13 @@ 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_INTR_COAL)) {
> +		vi->rx_usecs = 0;
> +		vi->tx_usecs = 0;
> +		vi->tx_frames_max = 0;
> +		vi->rx_frames_max = 0;
> +	}
> +
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_HASH_REPORT))
>  		vi->has_rss_hash_report = true;
> 
> @@ -3786,7 +3868,7 @@ 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_INTR_COAL
> 
>  static unsigned int features[] = {
>  	VIRTNET_FEATURES,
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index 3f55a4215f1..b65a4295270 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/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_INTR_COAL	55	/* Guest can handle Interrupt 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 interrupt coalescing.
> + *
> + * Request the device to change the interrupt coalescing parameters.
> + *
> + * Available with the VIRTIO_NET_F_INTR_COAL feature bit.
> + */
> +#define VIRTIO_NET_CTRL_INTR_COAL		6
> +/*
> + * Set the rx-usecs/tx-usecs patameters.
> + * rx-usecs - Number of microseconds to delay an RX interrupt after packet arrival.
> + * tx-usecs - Number of microseconds to delay a TX interrupt after a sending a packet.
> + */
> +struct virtio_net_ctrl_coal_usec {
> +	__u32 tx_usecs;
> +	__u32 rx_usecs;
> +};
> +
> +#define VIRTIO_NET_CTRL_INTR_COAL_USECS_SET		0
> +
> +/*
> + * Set the rx-max-frames/tx-max-frames patameters.
> + * rx-max-frames - Number of packets to delay an RX interrupt after packet arrival.
> + * tx-max-frames - Number of packets to delay a TX interrupt after sending a packet.
> + */
> +struct virtio_net_ctrl_coal_frames {
> +	__u32 tx_frames_max;
> +	__u32 rx_frames_max;
> +};
> +

You want all these to be LE. Native endian's unpredictable in lots of
virt settings.

> +#define VIRTIO_NET_CTRL_INTR_COAL_FRAMES_SET		1
> +
>  #endif /* _UAPI_LINUX_VIRTIO_NET_H */
> --
> 2.32.0