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From: Robert Watson <rwatson@FreeBSD.org>
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To: rihad <rihad@mail.ru>
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Cc: freebsd-net@freebsd.org
Subject: Re: dummynet dropping too many packets
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On Sat, 17 Oct 2009, rihad wrote:

>> Just rebooted with the "ifp->if_snd.ifq_drv_maxlen = 1024;" kernel, all ok 
>> so far. There's currenlty only 1000 or so entries in the ipfw table and 
>> around 350-400 net mbps load, so I'll wait a few hours for the numbers to 
>> grow to >2000 and 460-480 respectively and see if the drops still occur.
>
> The change definitely helped! There are now more than 3200 users online, 
> 460-500 mbps net traffic load, and normally 10-60 (up to 150 once or twice) 
> consistent drops per second as opposed to several hundred up to 1000-1500 
> packets dropped per second before the rebuild. What's interesting is that 
> the drops now began only after the ipfw table had around 3000 entries, not 
> 2000 like before, so the change definitely helped. Just how high can maxlen 
> be? Should I try 2048? 4096?

Sure, those should both be safe to use in your configuration, although as the 
numbers get higher, potential kernel memory use increases, as does the risk of 
starvation for clusters.  Keep an eye on "netstat -m" errors to see if you are 
reaching configured resouce limits (which you've probably increased already).

Robert