netdev - [PATCH net v2 0/2] cbq: incorrectly low bandwidth blocks limited traffic

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Date:	Thu, 14 Aug 2014 12:27:29 +0400
From:	Vasily Averin <vvs@...allels.com>
To:	netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>,
	"David S. Miller" <davem@...emloft.net>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>
Subject: [PATCH net v2 0/2] cbq: incorrectly low bandwidth blocks limited
 traffic

v2: patch description changes
Fixes: f0f6ee1f70c4 ("cbq: incorrect processing of high limits")

Mainstream commit f0f6ee1f70c4 ("cbq: incorrect processing of high limits")
have side effect: if cbq bandwidth setting is less than real interface
throughput non-limited traffic can delay limited traffic for a very long time.

This happen because of q->now changes incorrectly in cbq_dequeue():
in described scenario L2T is much greater than real time delay,
and q->now gets an extra boost for each transmitted packet.

Accumulated boost prevents update q->now, and blocked class can wait
very long time until (q->now >= cl->undertime) will be true again.

More detailed problem description can be found here:
http://www.spinics.net/lists/netdev/msg292493.html

Following patches should fix the problem.

Vasily Averin (2):
  cbq: incorrectly low bandwidth setting blocks limited traffic
  cbq: now_rt removal

 net/sched/sch_cbq.c |   48 ++++++++++++++----------------------------------
 1 files changed, 14 insertions(+), 34 deletions(-)

My testing confirmed that it fixes the problem and did not discover
any side-effects.
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