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

From: Jason Wang <[email-masked]>
Date: Tue, 10 Feb 2015 06:59:30 +0008

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.

> 
> 
> 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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