dummynet dropping too many packets

[rihad]

Eugene Grosbein wrote:
> On Mon, Oct 05, 2009 at 12:04:46PM +0200, Luigi Rizzo wrote:
> 
>>> The goal is to make sources of traffic to slow down, this is the only
>>> way to descrease drops - any finite queue may be overhelmed with traffic.
>>> Taildrop does not really help with this. GRED does much better.
>> i think the first problem here is figure out _why_ we have
>> the drops, as the original poster said that queues are configured
>> with a very large amount of buffer (and i think there is a
>> misconfiguration somewhere because the mbuf stats do not make
>> sense)
> 
> That may be very simple, f.e. wide uplink channel and policy that
> dictates slower client speeds. Any taildrop queue would drop lots
> of packets.
> 
If uplink is e.g. 100 mbit/s, but data is fed to client by dummynet at 1 
mbit/s, doesn't the _client's_ TCP software know to slow things down to 
not overwhelm 1 mbit/s? Where has TCP slow-start gone? My router box 
isn't some application proxy that starts downloading at full 100 mbit/s 
thus quickly filling client's 1 mbit/s link. It's just a router.

Although it doesn't yet make sense to me, I'll try going to GRED soon.