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

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Date:   Thu, 2 Aug 2018 18:57:46 +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 2018/08/02 18:23, Jason Wang wrote:
> On 2018年08月02日 16:41, Toshiaki Makita wrote:
>> On 2018/08/02 17:18, Jason Wang wrote:
>>> On 2018年08月01日 17:52, Tonghao Zhang wrote:
>>>>> +static void vhost_net_busy_poll_check(struct vhost_net *net,
>>>>> +                                   struct vhost_virtqueue *rvq,
>>>>> +                                   struct vhost_virtqueue *tvq,
>>>>> +                                   bool rx)
>>>>> +{
>>>>> +     struct socket *sock = rvq->private_data;
>>>>> +
>>>>> +     if (rx)
>>>>> +             vhost_net_busy_poll_try_queue(net, tvq);
>>>>> +     else if (sock && sk_has_rx_data(sock->sk))
>>>>> +             vhost_net_busy_poll_try_queue(net, rvq);
>>>>> +     else {
>>>>> +             /* On tx here, sock has no rx data, so we
>>>>> +              * will wait for sock wakeup for rx, and
>>>>> +              * vhost_enable_notify() is not needed. */
>>>> A possible case is we do have rx data but guest does not refill the rx
>>>> queue. In this case we may lose notifications from guest.
>>> Yes, should consider this case. thanks.
>> I'm a bit confused. Isn't this covered by the previous
>> "else if (sock && sk_has_rx_data(...))" block?
> 
> The problem is it does nothing if vhost_vq_avail_empty() is true and
> vhost_enble_notify() is false.

If vhost_enable_notify() is false, guest will eventually kicks vq, no?

-- 
Toshiaki Makita