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

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

[Vasily Averin]

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.

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

[David Miller]

From: Vasily Averin <vvs@parallels.com>
Date: Thu, 14 Aug 2014 12:27:29 +0400

> 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.

Series applied, thanks.