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Date: Fri, 3 Aug 2018 10:51:08 +0800 From: Tonghao Zhang <xiangxia.m.yue@...il.com> To: jasowang@...hat.com Cc: makita.toshiaki@....ntt.co.jp, 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 Thu, Aug 2, 2018 at 5:23 PM Jason Wang <jasowang@...hat.com> 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. > > > > >>>>> + > >>>>> + cpu_relax(); > >>>>> + } > >>>>> + > >>>>> + preempt_enable(); > >>>>> + > >>>>> + if (!rx) > >>>>> + vhost_net_enable_vq(net, vq); > >>>> 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. > > > > Yes. So we will use the vhost_has_work() to check whether or not the handle_rx is scheduled ? If we use the vhost_has_work(), the work in the dev work_list may be rx work, or tx work, right ? > Thanks
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