On 2018/07/24 2:31, Tonghao Zhang wrote:
> On Mon, Jul 23, 2018 at 10:20 PM Toshiaki Makita
> <toshiaki.makita1@xxxxxxxxx> wrote:
>>
>> On 18/07/23 (月) 21:43, Tonghao Zhang wrote:
>>> On Mon, Jul 23, 2018 at 5:58 PM Toshiaki Makita
>>> <makita.toshiaki@xxxxxxxxxxxxx> wrote:
>>>>
>>>> On 2018/07/22 3:04, xiangxia.m.yue@xxxxxxxxx wrote:
>>>>> From: Tonghao Zhang <xiangxia.m.yue@xxxxxxxxx>
>>>>>
>>>>> Factor out generic busy polling logic and will be
>>>>> used for in tx path in the next patch. And with the patch,
>>>>> qemu can set differently the busyloop_timeout for rx queue.
>>>>>
>>>>> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@xxxxxxxxx>
>>>>> ---
>>>> ...
>>>>> +static void vhost_net_busy_poll_vq_check(struct vhost_net *net,
>>>>> + struct vhost_virtqueue *rvq,
>>>>> + struct vhost_virtqueue *tvq,
>>>>> + bool rx)
>>>>> +{
>>>>> + struct socket *sock = rvq->private_data;
>>>>> +
>>>>> + if (rx) {
>>>>> + if (!vhost_vq_avail_empty(&net->dev, tvq)) {
>>>>> + vhost_poll_queue(&tvq->poll);
>>>>> + } else if (unlikely(vhost_enable_notify(&net->dev, tvq))) {
>>>>> + vhost_disable_notify(&net->dev, tvq);
>>>>> + vhost_poll_queue(&tvq->poll);
>>>>> + }
>>>>> + } else if ((sock && sk_has_rx_data(sock->sk)) &&
>>>>> + !vhost_vq_avail_empty(&net->dev, rvq)) {
>>>>> + vhost_poll_queue(&rvq->poll);
>>>>
>>>> Now we wait for vq_avail for rx as well, I think you cannot skip
>>>> vhost_enable_notify() on tx. Probably you might want to do:
>>> I think vhost_enable_notify is needed.
>>>
>>>> } else if (sock && sk_has_rx_data(sock->sk)) {
>>>> if (!vhost_vq_avail_empty(&net->dev, rvq)) {
>>>> vhost_poll_queue(&rvq->poll);
>>>> } else if (unlikely(vhost_enable_notify(&net->dev, rvq))) {
>>>> vhost_disable_notify(&net->dev, rvq);
>>>> vhost_poll_queue(&rvq->poll);
>>>> }
>>>> }
>>> As Jason review as before, we only want rx kick when packet is pending at
>>> socket but we're out of available buffers. So we just enable notify,
>>> but not poll it ?
>>>
>>> } else if ((sock && sk_has_rx_data(sock->sk)) &&
>>> !vhost_vq_avail_empty(&net->dev, rvq)) {
>>> vhost_poll_queue(&rvq->poll);
>>> else {
>>> vhost_enable_notify(&net->dev, rvq);
>>> }
>>
>> When vhost_enable_notify() returns true the avail becomes non-empty
>> while we are enabling notify. We may delay the rx process if we don't
>> check the return value of vhost_enable_notify().
> I got it thanks.
>>>> Also it's better to care vhost_net_disable_vq()/vhost_net_enable_vq() on tx?
>>> I cant find why it is better, if necessary, we can do it.
>>
>> The reason is pretty simple... we are busypolling the socket so we don't
>> need rx wakeups during it?
> OK, but one question, how about rx? do we use the
> vhost_net_disable_vq/vhost_net_ensable_vq on rx ?
If we are busypolling the sock tx buf? I'm not sure if polling it
improves the performance.
--
Toshiaki Makita
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