Re: [PATCH net-next] virtio-net: make napi_tx param easier to grasp

On Sun, 2017-08-20 at 16:30 -0400, Willem de Bruijn wrote:

On Sat, Aug 19, 2017 at 2:37 AM, Koichiro Den [off-list ref] wrote:

quoted

The module param napi_tx needs not to be writable for now since we do
not have any means of activating/deactivating it online,

A virtio_net device inherits its napi tx mode from the global napi_tx flag
on device up. It is possible to change the parameter and bring a device
down/up to change the device mode.

quoted

@@ -1179,13 +1172,19 @@ static int virtnet_open(struct net_device *dev)

        struct virtnet_info *vi = netdev_priv(dev);
        int i;

+       /* Tx napi touches cachelines on the cpu handling tx interrupts.
Only
+        * enable the feature if this is likely affine with the transmit
path.
+        */
+       if (!vi->affinity_hint_set)
+               napi_tx = false;
+

This disables napi globally if a specific device lacks affinity.

Now I see this is not appropriate since it just represents whether or not TX
napi is available, not that whether or not it is being turned on or off on a
particular device. Thank you.

To be honest I hoped to make it possible to see which mode it is currently
running on with ease, but I guess it's not nice to accomplish it with net sysfs
nor ethtool or whatever because it seems not much generic matter.

Thanks.

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