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

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Message-ID: <CACGkMEv4me_mjRJ8wEd-w_b9tjo370d6idioCTmFwJo-3TH3-A@mail.gmail.com>
Date: Fri, 22 Sep 2023 15:32:39 +0800
From: Jason Wang <jasowang@...hat.com>
To: Heng Qi <hengqi@...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>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Gavin Li <gavinl@...dia.com>
Subject: Re: [PATCH net 5/6] virtio-net: fix the vq coalescing setting for vq resize

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?

Thanks

>
> Thanks!
>
> >
> > Thanks
>