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>
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@ -1331,7 +1331,7 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
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}
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}
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if (rq->vq->num_free > virtqueue_get_vring_size(rq->vq) / 2) {
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if (rq->vq->num_free > min((unsigned int)budget, virtqueue_get_vring_size(rq->vq)) / 2) {
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if (!try_fill_recv(vi, rq, GFP_ATOMIC))
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schedule_delayed_work(&vi->refill, 0);
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}
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