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Date:      Sat, 28 Feb 2004 21:19:18 -0500
From:      Don Bowman <don@sandvine.com>
To:        'Deepak Jain' <deepak@ai.net>, freebsd-hackers@freebsd.org
Subject:   RE: em0, polling performance, P4 2.8ghz FSB 800mhz
Message-ID:  <FE045D4D9F7AED4CBFF1B3B813C85337045D8305@mail.sandvine.com>

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> I have a machine running 4.9.  P4 2.8Ghz, 800mhz bus, Intel PRO/1000 
> ethernet connected to a Cisco, both sides are locked to 1000/FD.
> 
> The kernel has HZ=1000, and DEVICE_POLLING, IPFW, DUMMYNET, 
> etc. After 
> only a few minutes of run time under an attack ~90,000 pps. 
> The attack 
> has been limited at the router to JUST incoming TCP port 80 inbound 
> traffic. I don't know why the machine is having such a hard 
> time under 
> the load. The cpu shows it is >90% idle even under the worst of the 
> attack.  What am I doing wrong?

I think there's a problem with CPU time not getting properly
accounted for in device polling, so it may be busier than you think.

For this scenario, i would set net.inet.tcp.blackhole=2. You
might be spending a lot of time creating the ICMP unreachable
messages, rather than in the network driver (where device polling
would help).

--don



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