Re: [PATCH net-next v3 4/4] net: vhost: add rx busy polling in tx path

[Jason Wang <jasowang@redhat.com>]

On 2018年06月30日 14:33, xiangxia.m.yue@gmail.com wrote:
> From: Tonghao Zhang <xiangxia.m.yue@gmail.com>
>
> This patch improves the guest receive and transmit performance.
> On the handle_tx side, we poll the sock receive queue at the
> same time. handle_rx do that in the same way.
>
> We set the poll-us=100us and use the iperf3 to test
> its bandwidth, use the netperf to test throughput and mean
> latency. When running the tests, the vhost-net kthread of
> that VM, is alway 100% CPU. The commands are shown as below.
>
> iperf3  -s -D
> iperf3  -c IP -i 1 -P 1 -t 20 -M 1400
>
> or
> netserver
> netperf -H IP -t TCP_RR -l 20 -- -O "THROUGHPUT,MEAN_LATENCY"
>
> host -> guest:
> iperf3:
> * With the patch:     27.0 Gbits/sec
> * Without the patch:  14.4 Gbits/sec
>
> netperf (TCP_RR):
> * With the patch:     48039.56 trans/s, 20.64us mean latency
> * Without the patch:  46027.07 trans/s, 21.58us mean latency
>
> This patch also improves the guest transmit performance.
>
> guest -> host:
> iperf3:
> * With the patch:     27.2 Gbits/sec
> * Without the patch:  24.4 Gbits/sec
>
> netperf (TCP_RR):
> * With the patch:     47963.25 trans/s, 20.71us mean latency
> * Without the patch:  45796.70 trans/s, 21.68us mean latency
>
> Signed-off-by: Tonghao Zhang <zhangtonghao@didichuxing.com>
> ---
>   drivers/vhost/net.c | 10 +++-------
>   1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 458f81d..fb43d82 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -478,17 +478,13 @@ static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
>   				    struct iovec iov[], unsigned int iov_size,
>   				    unsigned int *out_num, unsigned int *in_num)
>   {
> -	unsigned long uninitialized_var(endtime);
> +	struct vhost_net_virtqueue *nvq_rx = &net->vqs[VHOST_NET_VQ_RX];
>   	int r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
>   				  out_num, in_num, NULL, NULL);
>   
>   	if (r == vq->num && vq->busyloop_timeout) {
> -		preempt_disable();
> -		endtime = busy_clock() + vq->busyloop_timeout;
> -		while (vhost_can_busy_poll(vq->dev, endtime) &&
> -		       vhost_vq_avail_empty(vq->dev, vq))
> -			cpu_relax();
> -		preempt_enable();
> +		vhost_net_busy_poll(net, &nvq_rx->vq, vq, false);
> +
>   		r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
>   				      out_num, in_num, NULL, NULL);
>   	}

Looks good to me.

A nit is "rnvq" looks better.

Thanks

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