Re: [PATCH net-next v8 7/7] net: vhost: make busyloop_intr more accurate

[Jason Wang <jasowang@redhat.com>]

On 2018年08月19日 20:11, xiangxia.m.yue@gmail.com wrote:
> From: Tonghao Zhang <xiangxia.m.yue@gmail.com>
>
> The patch uses vhost_has_work_pending() to check if
> the specified handler is scheduled, because in the most case,
> vhost_has_work() return true when other side handler is added
> to worker list. Use the vhost_has_work_pending() insead of
> vhost_has_work().
>
> Topology:
> [Host] ->linux bridge -> tap vhost-net ->[Guest]
>
> TCP_STREAM (netperf):
> * Without the patch:  38035.39 Mbps, 3.37 us mean latency
> * With the patch:     38409.44 Mbps, 3.34 us mean latency

The improvement is not obvious as last version. Do you imply there's 
some recent changes of vhost that make it faster?

Thanks

>
> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
> ---
>   drivers/vhost/net.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index db63ae2..b6939ef 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -487,10 +487,8 @@ static void vhost_net_busy_poll(struct vhost_net *net,
>   	endtime = busy_clock() + busyloop_timeout;
>   
>   	while (vhost_can_busy_poll(endtime)) {
> -		if (vhost_has_work(&net->dev)) {
> -			*busyloop_intr = true;
> +		if (vhost_has_work(&net->dev))
>   			break;
> -		}
>   
>   		if ((sock_has_rx_data(sock) &&
>   		     !vhost_vq_avail_empty(&net->dev, rvq)) ||
> @@ -513,6 +511,11 @@ static void vhost_net_busy_poll(struct vhost_net *net,
>   	    !vhost_has_work_pending(&net->dev, VHOST_NET_VQ_RX))
>   		vhost_net_enable_vq(net, rvq);
>   
> +	if (vhost_has_work_pending(&net->dev,
> +				   poll_rx ?
> +				   VHOST_NET_VQ_RX: VHOST_NET_VQ_TX))
> +		*busyloop_intr = true;
> +
>   	mutex_unlock(&vq->mutex);
>   }
>