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

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Date:   Wed, 20 Jul 2022 15:02:04 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Alvaro Karsz <alvaro.karsz@...id-run.com>,
        netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v4] net: virtio_net: notifications coalescing support

On Wed, Jul 20, 2022 at 2:45 PM Michael S. Tsirkin <mst@...hat.com> 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 <alvaro.karsz@...id-run.com>
> >
> > Waiting a bit longer for Michael's ack, so in case other netdev
> > maintainer takes this:
> >
> > Reviewed-by: Jakub Kicinski <kuba@...nel.org>
>
> 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. For uAPI we know it should follow
the spec? (anyhow NAPI is something out of the spec)

Thanks

>
> --
> MST
>