netdev - Re: [PATCH net-next] virtio_net: ethtool tx napi configuration

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Message-ID: <cbc42263-0f2d-bf76-5842-e241dc1c97fb@redhat.com>
Date:   Mon, 10 Sep 2018 14:01:45 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, caleb.raitto@...il.com, mst@...hat.com,
        jonolson@...gle.com, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] virtio_net: ethtool tx napi configuration



On 2018年09月10日 06:44, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
>
> Implement ethtool .set_coalesce (-C) and .get_coalesce (-c) handlers.
> Interrupt moderation is currently not supported, so these accept and
> display the default settings of 0 usec and 1 frame.
>
> Toggle tx napi through a bit in tx-frames. So as to not interfere
> with possible future interrupt moderation, use bit 10, well outside
> the reasonable range of real interrupt moderation values.
>
> Changes are not atomic. The tx IRQ, napi BH and transmit path must
> be quiesced when switching modes. Only allow changing this setting
> when the device is down.

I cook a fixup, and it looks works in my setup:

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index b320b6b14749..9181c3f2f832 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2204,10 +2204,17 @@ static int virtnet_set_coalesce(struct 
net_device *dev,
                 return -EINVAL;

         if (napi_weight ^ vi->sq[0].napi.weight) {
-               if (dev->flags & IFF_UP)
-                       return -EBUSY;
-               for (i = 0; i < vi->max_queue_pairs; i++)
+               for (i = 0; i < vi->max_queue_pairs; i++) {
+                       struct netdev_queue *txq =
+                              netdev_get_tx_queue(vi->dev, i);
+
+ virtnet_napi_tx_disable(&vi->sq[i].napi);
+                       __netif_tx_lock_bh(txq);
                         vi->sq[i].napi.weight = napi_weight;
+                       __netif_tx_unlock_bh(txq);
+                       virtnet_napi_tx_enable(vi, vi->sq[i].vq,
+ &vi->sq[i].napi);
+               }
         }

         return 0;

The only left case is the speculative tx polling in RX NAPI. I think we 
don't need to care in this case since it was not a must for correctness.

>
> Link: https://patchwork.ozlabs.org/patch/948149/
> Suggested-by: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> ---
>   drivers/net/virtio_net.c | 52 ++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 52 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 765920905226..b320b6b14749 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -66,6 +66,8 @@ DECLARE_EWMA(pkt_len, 0, 64)
>   
>   #define VIRTNET_DRIVER_VERSION "1.0.0"
>   
> +static const u32 ethtool_coalesce_napi_mask = (1UL << 10);
> +
>   static const unsigned long guest_offloads[] = {
>   	VIRTIO_NET_F_GUEST_TSO4,
>   	VIRTIO_NET_F_GUEST_TSO6,
> @@ -2181,6 +2183,54 @@ static int virtnet_get_link_ksettings(struct net_device *dev,
>   	return 0;
>   }
>   
> +static int virtnet_set_coalesce(struct net_device *dev,
> +				struct ethtool_coalesce *ec)
> +{
> +	const struct ethtool_coalesce ec_default = {
> +		.cmd = ETHTOOL_SCOALESCE,
> +		.rx_max_coalesced_frames = 1,

I think rx part is no necessary.

Thanks

> +		.tx_max_coalesced_frames = 1,
> +	};
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	int i, napi_weight = 0;
> +
> +	if (ec->tx_max_coalesced_frames & ethtool_coalesce_napi_mask) {
> +		ec->tx_max_coalesced_frames &= ~ethtool_coalesce_napi_mask;
> +		napi_weight = NAPI_POLL_WEIGHT;
> +	}
> +
> +	/* disallow changes to fields not explicitly tested above */
> +	if (memcmp(ec, &ec_default, sizeof(ec_default)))
> +		return -EINVAL;
> +
> +	if (napi_weight ^ vi->sq[0].napi.weight) {
> +		if (dev->flags & IFF_UP)
> +			return -EBUSY;
> +		for (i = 0; i < vi->max_queue_pairs; i++)
> +			vi->sq[i].napi.weight = napi_weight;
> +	}
> +
> +	return 0;
> +}
> +
> +static int virtnet_get_coalesce(struct net_device *dev,
> +				struct ethtool_coalesce *ec)
> +{
> +	const struct ethtool_coalesce ec_default = {
> +		.cmd = ETHTOOL_GCOALESCE,
> +		.rx_max_coalesced_frames = 1,
> +		.tx_max_coalesced_frames = 1,
> +	};
> +	struct virtnet_info *vi = netdev_priv(dev);
> +
> +	memcpy(ec, &ec_default, sizeof(ec_default));
> +
> +	if (vi->sq[0].napi.weight)
> +		ec->tx_max_coalesced_frames |= ethtool_coalesce_napi_mask;
> +
> +	return 0;
> +}
> +
>   static void virtnet_init_settings(struct net_device *dev)
>   {
>   	struct virtnet_info *vi = netdev_priv(dev);
> @@ -2219,6 +2269,8 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
>   	.get_ts_info = ethtool_op_get_ts_info,
>   	.get_link_ksettings = virtnet_get_link_ksettings,
>   	.set_link_ksettings = virtnet_set_link_ksettings,
> +	.set_coalesce = virtnet_set_coalesce,
> +	.get_coalesce = virtnet_get_coalesce,
>   };
>   
>   static void virtnet_freeze_down(struct virtio_device *vdev)