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 10:29:17 +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 3:58 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>
>
>
> 在 2023/9/22 下午3:32, Jason Wang 写道:
> > 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?
>
> I'm not sure, ringsize has a wider range of changes. Maybe we should
> only keep coalescing
> parameters in cases where only vq_reset occurs (no ring size change
> involved)?

Probably but do we actually have a user other than resize now?

Thanks

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