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 10:47:47 +0800
From: Heng Qi <hengqi@...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>,
 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



在 2023/9/25 上午10:29, Jason Wang 写道:
> 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?

Not yet. What I mean is if there is one in the future, for example in 
xdp's processing etc.,
we can reserve parameters for it.

Thanks

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