Subject: Re: [PATCH net-next v4] net: virtio_net: notifications coalescing support

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 20 Jul 2022 03:05:01 -0400

On Wed, Jul 20, 2022 at 03:02:04PM +0800, Jason Wang wrote:
> On Wed, Jul 20, 2022 at 2:45 PM Michael S. Tsirkin <[email-masked]> wrote:
> >
> > On Tue, Jul 19, 2022 at 05:26:52PM -0700, Jakub Kicinski wrote:
> > > On Mon, 18 Jul 2022 12:11:02 +0300 Alvaro Karsz wrote:
> > > > New VirtIO network feature: VIRTIO_NET_F_NOTF_COAL.
> > > >
> > > > Control a Virtio network device notifications coalescing parameters
> > > > using the control virtqueue.
> > > >
> > > > A device that supports this fetature can receive
> > > > VIRTIO_NET_CTRL_NOTF_COAL control commands.
> > > >
> > > > - VIRTIO_NET_CTRL_NOTF_COAL_TX_SET:
> > > >   Ask the network device to change the following parameters:
> > > >   - tx_usecs: Maximum number of usecs to delay a TX notification.
> > > >   - tx_max_packets: Maximum number of packets to send before a
> > > >     TX notification.
> > > >
> > > > - VIRTIO_NET_CTRL_NOTF_COAL_RX_SET:
> > > >   Ask the network device to change the following parameters:
> > > >   - rx_usecs: Maximum number of usecs to delay a RX notification.
> > > >   - rx_max_packets: Maximum number of packets to receive before a
> > > >     RX notification.
> > > >
> > > > VirtIO spec. patch:
> > > > https://lists.oasis-open.org/archives/virtio-comment/202206/msg00100.html
> > > >
> > > > Signed-off-by: Alvaro Karsz <[email-masked]>
> > >
> > > Waiting a bit longer for Michael's ack, so in case other netdev
> > > maintainer takes this:
> > >
> > > Reviewed-by: Jakub Kicinski <[email-masked]>
> >
> > Yea was going to ack this but looking at the UAPI again we have a
> > problem because we abused tax max frames values 0 and 1 to control napi
> > in the past. technically does not affect legacy cards but userspace
> > can't easily tell the difference, can it?
> 
> The "abuse" only works for iproute2.

That's kernel/userspace API. That's what this patch affects, right?

> For uAPI we know it should follow
> the spec? (anyhow NAPI is something out of the spec)
> 
> Thanks

When you say uAPI here you mean the virtio header. I am not
worried about that just yet (maybe I should be).

> > --
> > MST