dummynet dropping too many packets

[Barney Cordoba]

--- On Tue, 10/20/09, rihad <rihad at mail.ru> wrote:

> From: rihad <rihad at mail.ru>
> Subject: Re: dummynet dropping too many packets
> To: freebsd-net at freebsd.org
> Date: Tuesday, October 20, 2009, 11:41 AM
> I'm so happy today: finally running a
> "ifp->if_snd.ifq_drv_maxlen = 4096;" and HZ=4000 kernel
> with 4100+ online users @500+ mbps, and, most importantly,
> with absolutely 0 drops since boot time! ;-) Even if drops
> do come in, I'll know where to look first. I'd like to
> express my gratitude to Robert Watson for pointing out the
> "ifnet transmit queue sizes" issue, to others who suggested
> the problem might be in dummynet's burstiness, and yet to
> others who tried hard to help with other suggestions. Thank
> you, folks! Tomorrow I'm going to suggest to my boss to
> donate some $$$ to the FreeBSD Foundation: http://www.freebsdfoundation.org/donate/

Seems to me that spending money on a real packetshaper would be a
better investment than donating to compromise on the free stuff (not 
that I'd want to discourage anyone from contributing to FreeBSD 
generally).

Your problem is that at high traffic levels you need to reduce traffic 
flows, not just delay it as dummynet does. The entire point of traffic
shaping is to smooth out your traffic flows; not to make it so choppy
that you have packets sitting in a transmit queue for 1/2 millisecond
in addition to the dummynet delays. While dummynet may not be dropping
packets, you have packets being dropped in TCP stacks throughout your
customer base, most likely.

Barney