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

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Message-ID: <1715064795.2147572-1-hengqi@linux.alibaba.com>
Date: Tue, 7 May 2024 14:53:15 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.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, 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?

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
> >
>