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 10:45:37 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...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>, 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 5:56 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>> 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.
> How did other drivers deal with this?

Test on mlx5, the behavior is the same as what this patch does:

#1 ethtool -g eth0
...
Current hardware settings:
RX: 8192
RX Mini: n/a
RX Jumbo: n/a
Tx: 1024
...

#2 ethtool -c eth0
Coalesce parameters for eth0:
Adaptive RX: off  TX: off
...
rx-usecs:    11
rx-frames:    32
rx-usecs-irq:    n/a
rx-frames-irq:    n/a
...

#3 sudo ethtool -G eth0 rx 4096
#4 ethtool -g eth0
Ring parameters for eth0:
...
Current hardware settings:
RX:        4096
RX Mini:    n/a
RX Jumbo:    n/a
TX:        1024
...

#4 ethtool -c eth0
Coalesce parameters for eth0:
Adaptive RX: off  TX: off
...
rx-usecs:    11
rx-frames:    32
rx-usecs-irq:    n/a
rx-frames-irq:    n/a
...

And I check the code, except for the parameters related to ring size, 
which are changed,
other parameters in structure mlx5e_params are retained.

Thanks

>
> Thanks
>
>> Thanks.
>>
>>
>>
>>
>>> Thanks
>>>
>>>> Thanks!
>>>>
>>>>> Thanks