Subject: Re: QoS hot changes changes (tc)

From: Jarek Poplawski <[email-masked]>
Date: Sat, 27 Jun 2009 23:42:26 +0200

Raúl Hernández wrote, On 06/26/2009 03:19 PM:

> Hi there,
> 
> I am trying to characterize the situation in which we perform a change
> in the shaping done by the Linux kernel (tc+qdisc), specifically when
> modifying the bandwidth as a hot change while shaping with a previous
> bw value. The system I am describing performs shaping per stream
> (uplink and/or dowinlink or total), just marking the TOS of the ip
> packet and provisioning the kernel via 'tc' to shape the packets.
> 
> My question is whether someone has tried to modify bw parameters, ie:
> move from 90 to 45 kb/s while the queues are already being populated
> with trafffic .Do not know if the shaper algorithm is able to adjust
> the bw without service disruption/experiment transitory behavior as I
> guess the algorithm must have some kind of feedback which depends of
> the bytes already shaped and the value of the bw itself (ie: leaky
> bucket).
> 
> Any experience with this kind of changes :-) ? Thx !

No experience in measuring the effects of such changes, but looking
into code shows it depends on a shaper algorithm: tbf seems to reset
the queue, htb doesn't.

Jarek P.