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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>
This commit is contained in:
? jiang 2019-08-20 02:51:23 +00:00 committed by Michael S. Tsirkin
parent 264b563b86
commit 718be6bab2
1 changed files with 1 additions and 1 deletions
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2
drivers/net/virtio_net.c
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@ -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);
}