Commit 718be6ba authored Aug 20, 2019 by ? jiang Committed by Michael S. Tsirkin Sep 04, 2019

virtio-net: lower min ring num_free for efficiency



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%)

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.

Signed-off-by: jiangkidd <jiangkidd@hotmail.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

parent 264b563b

drivers/net/virtio_net.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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);
		}

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