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cbq: incorrect processing of high limits
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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>
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Vasily Averin authored and David S. Miller committed Apr 2, 2013
1 parent bab6a9e commit f0f6ee1
Showing 1 changed file with 4 additions and 1 deletion.
5 changes: 4 additions & 1 deletion net/sched/sch_cbq.c
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Original file line number Diff line number Diff line change
Expand Up @@ -962,8 +962,11 @@ 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 (;;) {
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