vhost-net: set packet weight of tx polling to 2 * vq size
handle_tx will delay rx for tens or even hundreds of milliseconds when tx busy
polling udp packets with small length(e.g. 1byte udp payload), because setting
VHOST_NET_WEIGHT takes into account only sent-bytes but no single packet length.
Ping-Latencies shown below were tested between two Virtual Machines using
netperf (UDP_STREAM, len=1), and then another machine pinged the client:
Seems pretty consistent, a small dip at 2 VQ sizes.
Ring size is a hint from device about a burst size it can tolerate. Based on
benchmarks, set the weight to 2 * vq size.
To evaluate this change, another tests were done using netperf(RR, TX) between
two machines with Intel(R) Xeon(R) Gold 6133 CPU @ 2.50GHz, and vq size was
tweaked through qemu. Results shown below does not show obvious changes.
Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Haibin Zhang <haibinzhang@tencent.com> Signed-off-by: Yunfang Tai <yunfangtai@tencent.com> Signed-off-by: Lidong Chen <lidongchen@tencent.com> Signed-off-by: David S. Miller <davem@davemloft.net>