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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 10 Feb 2015 11:25:42 +0100

On Tue, Feb 10, 2015 at 06:59:30AM +0008, Jason Wang wrote:
> 
> 
> On Tue, Feb 10, 2015 at 9:32 AM, Rusty Russell <[email-masked]>
> wrote:
> >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]))
> 
> Yes. This looks better and we don't even need device specific configuration
> method.
> 
> >
> >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.
> 
> Can we give a device specific meaning for this? For virtio-net, we want to
> expose the coalescing settings through ethtool (tx-frames). And it was
> usually used with a timer, so probably another field after
> vring_used_delay() for this timer interval to trigger the interrupt if no
> new used buffers come after this interval.

I think what Rusty has in mind is precisely sticking the delay
in vring_used_delay.

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