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

Michael S. Tsirkin
2015-02-10T10:40:31Z

On Tue, Feb 10, 2015 at 12:02:37PM +1030, Rusty Russell wrote:
> Jason Wang <jasowang@redhat.com> 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.

But do we expect delay to be update dynamically?
If not, why not stick it in config space?

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

Yes, e.g. we can't extend config space for legacy virtio pci.

> > Cc: Rusty Russell <rusty@rustcorp.com.au>
> > Cc: Michael S. Tsirkin <mst@redhat.com>
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > ---
> > 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