netdev - Re: [PATCH net-next v7 3/4] net: vhost: factor out busy polling logic to vhost_net_busy

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Message-ID: <ace33be9-a004-f7be-4f73-911044eeae3f@redhat.com>
Date:   Fri, 3 Aug 2018 11:44:11 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        Tonghao Zhang <xiangxia.m.yue@...il.com>
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v7 3/4] net: vhost: factor out busy polling logic
 to vhost_net_busy_poll()



On 2018年08月03日 11:32, Toshiaki Makita wrote:
> On 2018/08/03 12:07, Jason Wang wrote:
>> On 2018年08月02日 17:23, Jason Wang wrote:
>>>>>>> No need to enable rx virtqueue, if we are sure handle_rx() will be
>>>>>>> called soon.
>>>>>> If we disable rx virtqueue in handle_tx and don't send packets from
>>>>>> guest anymore(handle_tx is not called), so we can wake up for sock rx.
>>>>>> so the network is broken.
>>>>> Not sure I understand here. I mean is we schedule work for handle_rx(),
>>>>> there's no need to enable it since handle_rx() will do this for us.
>>>> Looks like in the last "else" block in vhost_net_busy_poll_check() we
>>>> need to enable vq since in that case we have no rx data and handle_rx()
>>>> is not scheduled.
>>>>
>> Rethink about this, looks not. We enable rx wakeups in this case, so if
>> there's pending data, handle_rx() will be schedule after
>> vhost_net_enable_vq().
> You are right, but what I wanted to say is vhost_net_enable_vq() should
> be needed (I was talking about what would happen if
> vhost_net_enable_vq() were removed). Also, I think we should move
> vhost_net_enable_vq() from vhost_net_busy_poll() to this last "else"
> block because this is the case where rx wakeups is required.
> Anyway this part will be refactored so let's see what this code will
> look like in next version.
>

I get your point.

Thanks