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Date: Mon, 05 Oct 2009 16:47:59 +0500
From: rihad <rihad@mail.ru>
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Cc: freebsd-net@freebsd.org, Luigi Rizzo <rizzo@iet.unipi.it>
Subject: Re: dummynet dropping too many packets
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Eugene Grosbein wrote:
> On Mon, Oct 05, 2009 at 03:20:58PM +0500, rihad wrote:
> 
>>>>> 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?
> 
> That's not client's TCP software feeding your router with traffic
> but server side.
> 
Yup, I meant client-side decreasing congestion window, delaying ACKs 
etc. etc., typical for TCP congestion control. Or...?

GRED didn't solve the problem :(