From: Peilin Ye <peilin.ye@xxxxxxxxxxxxx>
Recently we introduced a Qdisc backpressure infrastructure (currently
supports UDP sockets). Use it in TBF Qdisc.
Tested with 500 Mbits/sec rate limit and SFQ inner Qdisc using 16 iperf UDP
1 Gbit/sec clients. Before:
[ 3] 0.0-15.0 sec 53.6 MBytes 30.0 Mbits/sec 0.208 ms 1190234/1228450 (97%)
[ 3] 0.0-15.0 sec 54.7 MBytes 30.6 Mbits/sec 0.085 ms 955591/994593 (96%)
[ 3] 0.0-15.0 sec 55.4 MBytes 31.0 Mbits/sec 0.170 ms 966364/1005868 (96%)
[ 3] 0.0-15.0 sec 55.0 MBytes 30.8 Mbits/sec 0.167 ms 925083/964333 (96%)
<...> ^^^^^^^^^^^^^^^^^^^
Total throughput is 480.2 Mbits/sec and average drop rate is 96.5%.
Now enable Qdisc backpressure for UDP sockets, with
udp_backpressure_interval default to 100 milliseconds:
[ 3] 0.0-15.0 sec 54.4 MBytes 30.4 Mbits/sec 0.097 ms 450/39246 (1.1%)
[ 3] 0.0-15.0 sec 54.4 MBytes 30.4 Mbits/sec 0.331 ms 435/39232 (1.1%)
[ 3] 0.0-15.0 sec 54.4 MBytes 30.4 Mbits/sec 0.040 ms 435/39212 (1.1%)
[ 3] 0.0-15.0 sec 54.4 MBytes 30.4 Mbits/sec 0.031 ms 426/39208 (1.1%)
<...> ^^^^^^^^^^^^^^^^
Total throughput is 486.4 Mbits/sec (1.29% higher) and average drop rate
is 1.1% (98.86% lower).
However, enabling Qdisc backpressure affects fairness between flow if we
use TBF Qdisc with default bfifo inner Qdisc:
[ 3] 0.0-15.0 sec 46.1 MBytes 25.8 Mbits/sec 1.102 ms 142/33048 (0.43%)
[ 3] 0.0-15.0 sec 72.8 MBytes 40.7 Mbits/sec 0.476 ms 145/52081 (0.28%)
[ 3] 0.0-15.0 sec 53.2 MBytes 29.7 Mbits/sec 1.047 ms 141/38086 (0.37%)
[ 3] 0.0-15.0 sec 45.5 MBytes 25.4 Mbits/sec 1.600 ms 141/32573 (0.43%)
<...> ^^^^^^^^^^^^^^^^^
In the test, per-flow throughput ranged from 16.4 to 68.7 Mbits/sec.
However, total throughput was still 486.4 Mbits/sec (0.87% higher than
before), and average drop rate was 0.41% (99.58% lower than before).
Signed-off-by: Peilin Ye <peilin.ye@xxxxxxxxxxxxx>
---
net/sched/sch_tbf.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
index 72102277449e..cf9cc7dbf078 100644
--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c
@@ -222,6 +222,7 @@ static int tbf_segment(struct sk_buff *skb, struct Qdisc *sch,
len += segs->len;
ret = qdisc_enqueue(segs, q->qdisc, to_free);
if (ret != NET_XMIT_SUCCESS) {
+ qdisc_backpressure(skb);
if (net_xmit_drop_count(ret))
qdisc_qstats_drop(sch);
} else {
@@ -250,6 +251,7 @@ static int tbf_enqueue(struct sk_buff *skb, struct Qdisc *sch,
}
ret = qdisc_enqueue(skb, q->qdisc, to_free);
if (ret != NET_XMIT_SUCCESS) {
+ qdisc_backpressure(skb);
if (net_xmit_drop_count(ret))
qdisc_qstats_drop(sch);
return ret;
--
2.20.1
