netdev - Re: [PATCH net-next v2 1/2] virtio_net: introduce ability to get reply info from device

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Message-ID: <CACGkMEtdk8L9jAh+9YAE0Nwwsd2_XXULU68mFn5Rje6f-MHWAw@mail.gmail.com>
Date: Wed, 8 May 2024 10:20:05 +0800
From: Jason Wang <jasowang@...hat.com>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, virtualization@...ts.linux.dev, 
	"Michael S . Tsirkin" <mst@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Eric Dumazet <edumazet@...gle.com>, "David S . Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v2 1/2] virtio_net: introduce ability to get
 reply info from device

On Tue, May 7, 2024 at 2:56 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>
> On Tue, 7 May 2024 14:24:19 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > On Fri, Apr 26, 2024 at 2:54 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
> > >
> > > From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > >
> > > As the spec https://github.com/oasis-tcs/virtio-spec/commit/42f389989823039724f95bbbd243291ab0064f82
> > >
> > > Based on the description provided in the above specification, we have
> > > enabled the virtio-net driver to support acquiring some response
> > > information from the device via the CVQ (Control Virtqueue).
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> >
> > I wonder if we need to tweak the spec as it has:
> >
> > """
> > Upon disabling and re-enabling a transmit virtqueue, the device MUST
> > set the coalescing parameters of the virtqueue
> > to those configured through the VIRTIO_NET_CTRL_NOTF_COAL_TX_SET
> > command, or, if the driver did not set any TX coalescing parameters,
> > to 0.
> > """
> >
> > So for reset, this patch tells us the device would have a non-zero
> > default value.
> >
> > But spec tolds us after vq reset, it has a zero default value ...
>
> Maybe we add a bool or flag for driver to mark whether the user has actively
> configured interrupt coalescing parameters. Then we can take actions when
> vq reset occurs?

I basically mean we probably need to tweak the spec. For example say
the device may have a default value for coalescing so driver need to
read them.

Thanks

>
> Thanks.
>
> >
> > Thanks
> >
> >
> > > ---
> > >  drivers/net/virtio_net.c | 24 +++++++++++++++++-------
> > >  1 file changed, 17 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 7176b956460b..3bc9b1e621db 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -2527,11 +2527,12 @@ static int virtnet_tx_resize(struct virtnet_info *vi,
> > >   * supported by the hypervisor, as indicated by feature bits, should
> > >   * never fail unless improperly formatted.
> > >   */
> > > -static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> > > -                                struct scatterlist *out)
> > > +static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd,
> > > +                                      struct scatterlist *out,
> > > +                                      struct scatterlist *in)
> > >  {
> > > -       struct scatterlist *sgs[4], hdr, stat;
> > > -       unsigned out_num = 0, tmp;
> > > +       struct scatterlist *sgs[5], hdr, stat;
> > > +       u32 out_num = 0, tmp, in_num = 0;
> > >         int ret;
> > >
> > >         /* Caller should know better */
> > > @@ -2549,10 +2550,13 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> > >
> > >         /* Add return status. */
> > >         sg_init_one(&stat, &vi->ctrl->status, sizeof(vi->ctrl->status));
> > > -       sgs[out_num] = &stat;
> > > +       sgs[out_num + in_num++] = &stat;
> > >
> > > -       BUG_ON(out_num + 1 > ARRAY_SIZE(sgs));
> > > -       ret = virtqueue_add_sgs(vi->cvq, sgs, out_num, 1, vi, GFP_ATOMIC);
> > > +       if (in)
> > > +               sgs[out_num + in_num++] = in;
> > > +
> > > +       BUG_ON(out_num + in_num > ARRAY_SIZE(sgs));
> > > +       ret = virtqueue_add_sgs(vi->cvq, sgs, out_num, in_num, vi, GFP_ATOMIC);
> > >         if (ret < 0) {
> > >                 dev_warn(&vi->vdev->dev,
> > >                          "Failed to add sgs for command vq: %d\n.", ret);
> > > @@ -2574,6 +2578,12 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> > >         return vi->ctrl->status == VIRTIO_NET_OK;
> > >  }
> > >
> > > +static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
> > > +                                struct scatterlist *out)
> > > +{
> > > +       return virtnet_send_command_reply(vi, class, cmd, out, NULL);
> > > +}
> > > +
> > >  static int virtnet_set_mac_address(struct net_device *dev, void *p)
> > >  {
> > >         struct virtnet_info *vi = netdev_priv(dev);
> > > --
> > > 2.32.0.3.g01195cf9f
> > >
> >
>