[PATCH v2] virtio-net: lower min ring num_free for efficiency

[PATCH v2] virtio-net: lower min ring num_free for efficiency

[? jiang]

This change lowers ring buffer reclaim threshold from 1/2*queue to budget
for better performance. According to our test with qemu + dpdk, packet
dropping happens when the guest is not able to provide free buffer in
avail ring timely with default 1/2*queue. The value in the patch has been
tested and does show better performance.

Test setup: iperf3 to generate packets to guest (total 30mins, pps 400k, UDP)
avg packets drop before: 2842
avg packets drop after: 360(-87.3%)

Signed-off-by: jiangkidd <jiangkidd@hotmail.com>
---
 drivers/net/virtio_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0d4115c9e20b..bc08be7925eb 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1331,7 +1331,7 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
 		}
 	}
 
-	if (rq->vq->num_free > virtqueue_get_vring_size(rq->vq) / 2) {
+	if (rq->vq->num_free > min((unsigned int)budget, virtqueue_get_vring_size(rq->vq)) / 2) {
 		if (!try_fill_recv(vi, rq, GFP_ATOMIC))
 			schedule_delayed_work(&vi->refill, 0);
 	}
-- 
2.11.0

Re: [PATCH v2] virtio-net: lower min ring num_free for efficiency

[Jason Wang]

On 2019/8/15 下午5:42, ? jiang wrote:
> This change lowers ring buffer reclaim threshold from 1/2*queue to budget
> for better performance. According to our test with qemu + dpdk, packet
> dropping happens when the guest is not able to provide free buffer in
> avail ring timely with default 1/2*queue. The value in the patch has been
> tested and does show better performance.
>
> Test setup: iperf3 to generate packets to guest (total 30mins, pps 400k, UDP)
> avg packets drop before: 2842
> avg packets drop after: 360(-87.3%)
>
> Signed-off-by: jiangkidd <jiangkidd@hotmail.com>
> ---
>   drivers/net/virtio_net.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0d4115c9e20b..bc08be7925eb 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1331,7 +1331,7 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
>   		}
>   	}
>   
> -	if (rq->vq->num_free > virtqueue_get_vring_size(rq->vq) / 2) {
> +	if (rq->vq->num_free > min((unsigned int)budget, virtqueue_get_vring_size(rq->vq)) / 2) {
>   		if (!try_fill_recv(vi, rq, GFP_ATOMIC))
>   			schedule_delayed_work(&vi->refill, 0);
>   	}


Acked-by: Jason Wang <jasowang@redhat.com>


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Re: [PATCH v2] virtio-net: lower min ring num_free for efficiency

[Michael S. Tsirkin]

On Thu, Aug 15, 2019 at 09:42:40AM +0000, ? jiang wrote:
> This change lowers ring buffer reclaim threshold from 1/2*queue to budget
> for better performance. According to our test with qemu + dpdk, packet
> dropping happens when the guest is not able to provide free buffer in
> avail ring timely with default 1/2*queue. The value in the patch has been
> tested and does show better performance.
> 
> Test setup: iperf3 to generate packets to guest (total 30mins, pps 400k, UDP)
> avg packets drop before: 2842
> avg packets drop after: 360(-87.3%)
> 
> Signed-off-by: jiangkidd <jiangkidd@hotmail.com>

To add to that:

Further, current code suffers from a starvation problem: the amount of
work done by try_fill_recv is not bounded by the budget parameter, thus
(with large queues) once in a while userspace gets blocked for a long
time while queue is being refilled. Trigger refills earlier to make sure
the amount of work to do is limited.

With this addition to the log:

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  drivers/net/virtio_net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0d4115c9e20b..bc08be7925eb 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1331,7 +1331,7 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
>  		}
>  	}
>  
> -	if (rq->vq->num_free > virtqueue_get_vring_size(rq->vq) / 2) {
> +	if (rq->vq->num_free > min((unsigned int)budget, virtqueue_get_vring_size(rq->vq)) / 2) {
>  		if (!try_fill_recv(vi, rq, GFP_ATOMIC))
>  			schedule_delayed_work(&vi->refill, 0);
>  	}
> -- 
> 2.11.0