Subject: Re: [PATCH RFC v5 net-next 4/6] virtio-net: add basic interrupt coalescing support

From: Rusty Russell <[email-masked]>
Date: Tue, 10 Feb 2015 12:02:37 +1030

Jason Wang <[email-masked]> writes:
> This patch enables the interrupt coalescing setting through ethtool.

The problem is that there's nothing network specific about interrupt
coalescing.  I can see other devices wanting exactly the same thing,
which means we'd deprecate this in the next virtio standard.

I think the right answer is to extend like we did with
vring_used_event(), eg:

1) Add a new feature VIRTIO_F_RING_COALESCE.
2) Add another a 32-bit field after vring_used_event(), eg:
        #define vring_used_delay(vr) (*(u32 *)((vr)->avail->ring[(vr)->num + 2]))

This loses the ability to coalesce by number of frames, but we can still
do number of sg entries, as we do now with used_event, and we could
change virtqueue_enable_cb_delayed() to take a precise number if we
wanted.

My feeling is that this should be a v1.0-only feature though
(eg. feature bit 33).

Cheers,
Rusty.

> Cc: Rusty Russell <[email-masked]>
> Cc: Michael S. Tsirkin <[email-masked]>
> Signed-off-by: Jason Wang <[email-masked]>
> ---
>  drivers/net/virtio_net.c        | 67 +++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_net.h | 12 ++++++++
>  2 files changed, 79 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index cc5f5de..2b958fb 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -145,6 +145,11 @@ struct virtnet_info {
>  
>  	/* Budget for polling tx completion */
>  	u32 tx_work_limit;
> +
> +	__u32 rx_coalesce_usecs;
> +	__u32 rx_max_coalesced_frames;
> +	__u32 tx_coalesce_usecs;
> +	__u32 tx_max_coalesced_frames;
>  };
>  
>  struct padded_vnet_hdr {
> @@ -1404,12 +1409,73 @@ static void virtnet_get_channels(struct net_device *dev,
>  	channels->other_count = 0;
>  }
>  
> +static int virtnet_set_coalesce(struct net_device *dev,
> +				struct ethtool_coalesce *ec)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	struct scatterlist sg;
> +	struct virtio_net_ctrl_coalesce c;
> +
> +	if (!vi->has_cvq ||
> +	    !virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_COALESCE))
> +		return -EOPNOTSUPP;
> +	if (vi->rx_coalesce_usecs != ec->rx_coalesce_usecs ||
> +	    vi->rx_max_coalesced_frames != ec->rx_max_coalesced_frames) {
> +		c.coalesce_usecs = ec->rx_coalesce_usecs;
> +		c.max_coalesced_frames = ec->rx_max_coalesced_frames;
> +		sg_init_one(&sg, &c, sizeof(c));
> +		if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_COALESCE,
> +					  VIRTIO_NET_CTRL_COALESCE_RX_SET,
> +					  &sg)) {
> +			dev_warn(&dev->dev, "Fail to set rx coalescing\n");
> +			return -EINVAL;
> +		}
> +		vi->rx_coalesce_usecs = ec->rx_coalesce_usecs;
> +		vi->rx_max_coalesced_frames = ec->rx_max_coalesced_frames;
> +	}
> +
> +	if (vi->tx_coalesce_usecs != ec->tx_coalesce_usecs ||
> +	    vi->tx_max_coalesced_frames != ec->tx_max_coalesced_frames) {
> +		c.coalesce_usecs = ec->tx_coalesce_usecs;
> +		c.max_coalesced_frames = ec->tx_max_coalesced_frames;
> +		sg_init_one(&sg, &c, sizeof(c));
> +		if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_COALESCE,
> +					  VIRTIO_NET_CTRL_COALESCE_TX_SET,
> +					  &sg)) {
> +			dev_warn(&dev->dev, "Fail to set tx coalescing\n");
> +			return -EINVAL;
> +		}
> +		vi->tx_coalesce_usecs = ec->tx_coalesce_usecs;
> +		vi->tx_max_coalesced_frames = ec->tx_max_coalesced_frames;
> +	}
> +
> +	vi->tx_work_limit = ec->tx_max_coalesced_frames_irq;
> +
> +	return 0;
> +}
> +
> +static int virtnet_get_coalesce(struct net_device *dev,
> +				struct ethtool_coalesce *ec)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +
> +	ec->rx_coalesce_usecs = vi->rx_coalesce_usecs;
> +	ec->rx_max_coalesced_frames = vi->rx_max_coalesced_frames;
> +	ec->tx_coalesce_usecs = vi->tx_coalesce_usecs;
> +	ec->tx_max_coalesced_frames = vi->tx_max_coalesced_frames;
> +	ec->tx_max_coalesced_frames_irq = vi->tx_work_limit;
> +
> +	return 0;
> +}
> +
>  static const struct ethtool_ops virtnet_ethtool_ops = {
>  	.get_drvinfo = virtnet_get_drvinfo,
>  	.get_link = ethtool_op_get_link,
>  	.get_ringparam = virtnet_get_ringparam,
>  	.set_channels = virtnet_set_channels,
>  	.get_channels = virtnet_get_channels,
> +	.set_coalesce = virtnet_set_coalesce,
> +	.get_coalesce = virtnet_get_coalesce,
>  };
>  
>  #define MIN_MTU 68
> @@ -2048,6 +2114,7 @@ static unsigned int features[] = {
>  	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ,
>  	VIRTIO_NET_F_CTRL_MAC_ADDR,
>  	VIRTIO_F_ANY_LAYOUT,
> +	VIRTIO_NET_F_CTRL_COALESCE,
>  };
>  
>  static struct virtio_driver virtio_net_driver = {
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index b5f1677..332009d 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -34,6 +34,7 @@
>  /* The feature bitmap for virtio net */
>  #define VIRTIO_NET_F_CSUM	0	/* Host handles pkts w/ partial csum */
>  #define VIRTIO_NET_F_GUEST_CSUM	1	/* Guest handles pkts w/ partial csum */
> +#define VIRTIO_NET_F_CTRL_COALESCE 3	/* Set coalescing */
>  #define VIRTIO_NET_F_MAC	5	/* Host has given MAC address. */
>  #define VIRTIO_NET_F_GSO	6	/* Host handles pkts w/ any GSO type */
>  #define VIRTIO_NET_F_GUEST_TSO4	7	/* Guest can handle TSOv4 in. */
> @@ -202,4 +203,15 @@ struct virtio_net_ctrl_mq {
>   #define VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MIN        1
>   #define VIRTIO_NET_CTRL_MQ_VQ_PAIRS_MAX        0x8000
>  
> +struct virtio_net_ctrl_coalesce {
> +	__u32 coalesce_usecs;
> +	__u32 max_coalesced_frames;
> +};
> +
> +#define VIRTIO_NET_CTRL_COALESCE 6
> + #define VIRTIO_NET_CTRL_COALESCE_TX_SET 0
> + #define VIRTIO_NET_CTRL_COALESCE_TX_GET 1
> + #define VIRTIO_NET_CTRL_COALESCE_RX_SET 2
> + #define VIRTIO_NET_CTRL_COALESCE_RX_GET 3
> +
>  #endif /* _LINUX_VIRTIO_NET_H */
> -- 
> 1.8.3.1