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

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Date: Fri, 22 Sep 2023 17:50:43 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.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, 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.

Thanks.

>
> Thanks
>
> >
> > Thanks!
> >
> > >
> > > Thanks
> >
>