I am trying to do ingress flow control with htb + imq,
and as could be expected it isn't working well.
It works a lot better when I keep the htb ceiling well
below what the link can actually carry - I guess because
htb gets to throttle the TCP fast start before it causes
packets to be dropped. The only problem is wasting all
that bandwidth hurts.
It occurred to me that the bandwidth needn't be wasted,
if only I can convince HTB to reserve some bandwidth
for a class.
For example, lets say we have a 1000kbit link, and two
classes sharing that link:
- Voip - ie high prio real time, and
- Web - background traffic.
Right now, with htb or cbq or whatever, I can do this:
Guaranteed Rate Ceiling Prio
Link 700kbit 700kbit
|--Voip 200kbit 700kbit 1
\--Web 300kbit 700kbit 2
This works, in that Voip won't be hit by new connections
overloading the link before htb can bring then under
control. But it wastes 300kbit of bandwidth in doing
so.
An observation. Lets say the link is carrying its rated
capacity. Ie, there is 400kbit of Voip traffic, and
300kbit of web traffic. In this scenario, there is
really no harm letting the Voip use the remaining 300kbit
of spare capacity. The Voip traffic is already being
shaped so delays are being introduced by the HTB filter
anyway. If we let it use the remaining 300kb that shaping
may disappear. Yes, it may now be hit by new incoming TCP
traffic - but we may get lucky and it may not, whereas
before it was always being shaped by HTB.
To be more precise, I want to create some "headroom" that
VOIP can use, but Web traffic can't. Here are some
examples. In each case the link is maxed out.
Packets arriving at filter Packets sent by Filter
Voip Web Voip Web
0 BIG 0 700kbit
200kbit BIG 200kbit 500kbit
400kbit BIG 400kbit 300kbit
600kbit BIG 600kbit 300kbit
BIG BIG 700kbit 300kbit
As far as I can tell, HTB, nor any other qdisc for that
matter, can be configured to do this. Am I correct?
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