traffic bandwidth limit with dummynet

[Luigi Rizzo]

On Thu, Jun 03, 2010 at 09:29:20AM -0700, bored to death wrote:
> hello,
> 
> i'm trying to limit my input traffic bandwidth on freebsd. i used
> ipfw+dummynet. without limitation, i have almost 1Gbit/s input traffic
> on my system. when i try to limit the bandwidth, it works fine on low
> to normal limitation number (up to 450 Mbit/s).
> but when i limit my traffic to an amount bigger than 500MBit/s, my
> input traffic lowers down to average of 430 MBit/s. no matter what
> limitations i set(from 500MBit/s to 1000MBit/s) my input traffic rate
> is getting stucked at 430MBit/s. 

try to run the kernel with higher value of HZ (in /boot/loader.conf

	kern.hz=4000

and see if the situation improves.
I think the symptoms you are seeing depend on the fact that
packets are released every 1/HZ seconds probably causing some
queue overflow at high packet rates and [relatively] low HZ
values.

cheers
luigi

> i suspected low hardware performance, so i tried this on 2 different
> systems with freebsd-8.0 and the result is exactly the same.
> 
> my ipfw rules are:
> 
> Code:
> ipfw -q flush
> ipfw -q add 500 set 1 pipe 1 all from any to any in
> ipfw pipe 1 config bw 700Mbit/s
> ipfw add 1000 allow all from any to anyso my question is:
> 1- is ipfw+dummynet traffic limit control, has performance problem that
> cannot limit traffic correctly if limitation number is bigger than
> 500MBit/s?
> 2- is there any other way (other than ipfw+dummynet) to limit input bandwidth in freebsd?
> 
> thank you. 
> 
> 
>       
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