[109/126] cbq: incorrect processing of high limits

Steven Rostedt
2013-05-07T04:40:20Z

[-- Attachment #1: 0109-cbq-incorrect-processing-of-high-limits.patch --]
[-- Type: text/plain, Size: 1572 bytes --]

3.6.11.3 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Vasily Averin <vvs@parallels.com>

[ Upstream commit f0f6ee1f70c4eaab9d52cf7d255df4bd89f8d1c2 ]

currently cbq works incorrectly for limits > 10% real link bandwidth,
and practically does not work for limits > 50% real link bandwidth.
Below are results of experiments taken on 1 Gbit link

In shaper | Actual Result
-----------+---------------
100M | 108 Mbps
200M | 244 Mbps
300M | 412 Mbps
500M | 893 Mbps

This happen because of q->now changes incorrectly in cbq_dequeue():
when it is called before real end of packet transmitting,
L2T is greater than real time delay, q_now gets an extra boost
but never compensate it.

To fix this problem we prevent change of q->now until its synchronization
with real time.

Signed-off-by: Vasily Averin <vvs@openvz.org>
Reviewed-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
net/sched/sch_cbq.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
index 564b9fc..611d5e9 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -963,8 +963,11 @@ cbq_dequeue(struct Qdisc *sch)
cbq_update(q);
if ((incr -= incr2) < 0)
incr = 0;
+ q->now += incr;
+ } else {
+ if (now > q->now)
+ q->now = now;
}
- q->now += incr;
q->now_rt = now;

for (;;) {
--
1.7.10.4