netdev - Re: [PATCH net-next v5 3/4] net: vhost: factor out busy polling logic to vhost_net_busy

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Date:   Wed, 4 Jul 2018 17:46:12 +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>,
        Tonghao Zhang <zhangtonghao@...ichuxing.com>
Subject: Re: [PATCH net-next v5 3/4] net: vhost: factor out busy polling logic
 to vhost_net_busy_poll()

On Wed, Jul 4, 2018 at 5:18 PM Jason Wang <jasowang@...hat.com> wrote:
>
>
>
> On 2018年07月04日 15:59, Toshiaki Makita wrote:
> > On 2018/07/04 13:31, xiangxia.m.yue@...il.com wrote:
> > ...
> >> +static void vhost_net_busy_poll(struct vhost_net *net,
> >> +                            struct vhost_virtqueue *rvq,
> >> +                            struct vhost_virtqueue *tvq,
> >> +                            bool rx)
> >> +{
> >> +    unsigned long uninitialized_var(endtime);
> >> +    unsigned long busyloop_timeout;
> >> +    struct socket *sock;
> >> +    struct vhost_virtqueue *vq = rx ? tvq : rvq;
> >> +
> >> +    mutex_lock_nested(&vq->mutex, rx ? VHOST_NET_VQ_TX: VHOST_NET_VQ_RX);
> >> +
> >> +    vhost_disable_notify(&net->dev, vq);
> >> +    sock = rvq->private_data;
> >> +    busyloop_timeout = rx ? rvq->busyloop_timeout : tvq->busyloop_timeout;
> >> +
> >> +    preempt_disable();
> >> +    endtime = busy_clock() + busyloop_timeout;
> >> +    while (vhost_can_busy_poll(tvq->dev, endtime) &&
> >> +           !(sock && sk_has_rx_data(sock->sk)) &&
> >> +           vhost_vq_avail_empty(tvq->dev, tvq))
> >> +            cpu_relax();
> >> +    preempt_enable();
> >> +
> >> +    if ((rx && !vhost_vq_avail_empty(&net->dev, vq)) ||
> >> +        (!rx && (sock && sk_has_rx_data(sock->sk)))) {
> >> +            vhost_poll_queue(&vq->poll);
> >> +    } else if (vhost_enable_notify(&net->dev, vq) && rx) {
> > Hmm... on tx here sock has no rx data, so you are waiting for sock
> > wakeup for rx and vhost_enable_notify() seems not needed. Do you want
> > this actually?
> >
> > } else if (rx && vhost_enable_notify(&net->dev, vq)) {
>
> Right, rx need to be checked first here.
thanks， if we dont call the vhost_enable_notify for tx. so we dont
need to call vhost_disable_notify for tx?

@@ -451,7 +451,9 @@ static void vhost_net_busy_poll(struct vhost_net *net,
                                              tvq->busyloop_timeout;

        mutex_lock_nested(&vq->mutex, rx ? VHOST_NET_VQ_TX: VHOST_NET_VQ_RX);
-       vhost_disable_notify(&net->dev, vq);
+
+       if (rx)
+               vhost_disable_notify(&net->dev, vq);

        preempt_disable();
        endtime = busy_clock() + busyloop_timeout;

> Thanks
>
> >> +            vhost_disable_notify(&net->dev, vq);
> >> +            vhost_poll_queue(&vq->poll);
> >> +    }
>