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

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Date:   Fri, 3 Aug 2018 12:32:22 +0900
From:   Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:     Jason Wang <jasowang@...hat.com>,
        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 2018/08/03 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.

-- 
Toshiaki Makita