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Date: Sun, 19 Oct 2008 21:22:20 +0800
From: Eugene Grosbein <eugen@kuzbass.ru>
To: Hartmut Brandt <hartmut.brandt@dlr.de>
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Cc: net@freebsd.org
Subject: Re: SNMP High Capacity Counters
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On Sun, Oct 19, 2008 at 01:17:13PM +0200, Hartmut Brandt wrote:

> The problem is not the CPU horsepower. The problem is that you update 
> these counters on each incoming packet. No problem for desktops, but if 
> you want to route several 100kps this may hurt. I have no idea, how IPFW 
> does it. Perhaps it just declares the variables as 64-bit and if the 
> value is wrong because of a race condition, then it is just wrong. With 
> SNMP I would not like to have wrong counters - people use these counters 
> for accounting purposes.

IPFW defines its counters as u_int64_t and uses mtx_lock/mtx_unlock
while updating. Basically, this means lots of locking for every packet
for IPFW-enables system. I do not say we need 64 bit stats in kernel
by default. Just optionally, for those that have no problem with pps
but likes to have 64 bit ifHC*'s.

Eugene Grosbein