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

[Heng Qi <hengqi@linux.alibaba.com>]

在 2023/9/22 下午3:32, Jason Wang 写道:
> On Fri, Sep 22, 2023 at 1:02 PM Heng Qi <hengqi@linux.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@linux.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)?

Thanks!

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