netdev - Re: [PATCH net 5/6] virtio-net: fix the vq coalescing setting for vq resize

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Date: Mon, 25 Sep 2023 10:29:57 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org, 
	"Michael S . Tsirkin" <mst@...hat.com>, "David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, 
	John Fastabend <john.fastabend@...il.com>, Gavin Li <gavinl@...dia.com>, 
	Heng Qi <hengqi@...ux.alibaba.com>
Subject: Re: [PATCH net 5/6] virtio-net: fix the vq coalescing setting for vq resize

On Fri, Sep 22, 2023 at 5:56 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> On Fri, 22 Sep 2023 15:32:39 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > On Fri, Sep 22, 2023 at 1:02 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
> > >
> > >
> > >
> > > 在 2023/9/22 下午12:29, Jason Wang 写道:
> > > > On Tue, Sep 19, 2023 at 3:49 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
> > > >> According to the definition of virtqueue coalescing spec[1]:
> > > >>
> > > >>    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.
> > > >>
> > > >>    Upon disabling and re-enabling a receive virtqueue, the device MUST set
> > > >>    the coalescing parameters of the virtqueue to those configured through the
> > > >>    VIRTIO_NET_CTRL_NOTF_COAL_RX_SET command, or, if the driver did not set
> > > >>    any RX coalescing parameters, to 0.
> > > >>
> > > >> We need to add this setting for vq resize (ethtool -G) where vq_reset happens.
> > > >>
> > > >> [1] https://lists.oasis-open.org/archives/virtio-dev/202303/msg00415.html
> > > >>
> > > >> Fixes: 394bd87764b6 ("virtio_net: support per queue interrupt coalesce command")
> > > > I'm not sure this is a real fix as spec allows it to go zero?
> > >
> > > The spec says that if the user has configured interrupt coalescing
> > > parameters,
> > > parameters need to be restored after vq_reset, otherwise set to 0.
> > > vi->intr_coal_tx and vi->intr_coal_rx always save the newest global
> > > parameters,
> > > regardless of whether the command is sent or not. So I think we need
> > > this patch
> > > it complies with the specification requirements.
> >
> > How can we make sure the old coalescing parameters still make sense
> > for the new ring size?
>
> For the user, I don't think we should drop the config for the coalescing.
> Maybe the config does not make sense for the new ring size, but when the user
> just change the ring size, the config for the coalesing is missing, I think
> that is not good.

How did other drivers deal with this?

Thanks

>
> Thanks.
>
>
>
>
> >
> > Thanks
> >
> > >
> > > Thanks!
> > >
> > > >
> > > > Thanks
> > >
> >
>