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

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Message-ID: <6ca28b13-637e-8650-30a4-bb3f2ea96852@redhat.com>
Date:   Wed, 4 Jul 2018 17:18:09 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        xiangxia.m.yue@...il.com
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        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 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

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