[altq 224] Re: Kernel Ticks & Limits?

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

Karl Pielorz wrote:
> We've been running Altq 2.0 for a couple of months now... The old system we
> had was running Altq with the FreeBSD kernel ticks set to 1000 (instead of the
> default 100).
> 
> As the links we've used AltQ with had got faster since then - when we moved to
> 2.0 we also decided to go with the default Kernel tick rate
> 
> One problem we seem to have is that where the previous AltQ would keep a
> 128kbs (25% of 512kbs) at practically dead on it's 16 KByte/sec maximum, Altq
> 2.0 running with 100 HZ seems to be a bit lienent, we've see 128Kbs limits
> exceeded to 20 KByte/sec, i.e. 160 Kbs (31% of 512kbs).
> 
> The link in question is a 512kbs link - should we still be running with
> HZ=1000 in the kernel?

You don't need a high resolution timer for 512Kbps link.
A 1500 byte-packet takes 25msec on a 512Kbps link, and it's big enough
for 100Hz.

> Are there any other settings we can try to minimize this? - Don't get me
> wrong, 160kbs vs. 128kbs is still pretty good, but it doesn't seem to be as
> good as it used to be :-)

It could be caused by a minor change in the CBQ algorithm, or by a
change in the driver.  Is it fxp?

-Kenjiro