[altq 1295] Re: The more traffic come, the less delay.

[Kenjiro Cho <kjc@csl.sony.co.jp>]

Hiroyuki KATO wrote:
> when real-time traffic was incresed to 5Mbps,
> a congestion was occured and the time-delay was increased 
> to approximately 50ms.
> I am pretty sure that it happened because of queueing descipline. 

Not only the queueing discipline but also the buffer in the network
card increases the delay.
You can tune the token bucket regulator to minimize the delay.
See 1.7.2 of TIPS.txt.

> However, when real-time traffic was increased to 6Mbps,
> the time-delay was decresed from 50ms down to 40ms.
> 
> I do not know why this happened.
> I would appreciate if someone gives me a comment about it!

ALTQ tries to trigger the next transmission from interrupts and, if it
fails, falls back to the kernel timer.
When the assigned rate is 5Mbps, an interrupt occurs too early to send
the next packet, and CBQ has to wait for the timer tick (10ms interval
by default).
When the rate is increased to 6Mbps, an interrupt is allowed to
trigger the next packet transmission.

-Kenjiro