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

Jason Wang
2015-02-10T06:51:46Z

On Tue, Feb 10, 2015 at 9:32 AM, Rusty Russell <rusty@rustcorp.com.au>
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]))

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.

>
>
> 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 <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
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