cbq: incorrect processing of high limits
authorVasily Averin <vvs@parallels.com>
Mon, 1 Apr 2013 03:01:32 +0000 (03:01 +0000)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 1 May 2013 16:41:06 +0000 (09:41 -0700)
commit815b1018620edb2f86fc7a7740b9a0e726446929
treeca42f78750875df5b2fd4ff4e10588768f750042
parent7b806e764b487cf1f348d1e4377f99853935ff7c
cbq: incorrect processing of high limits

[ 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
net/sched/sch_cbq.c