em0, polling performance, P4 2.8ghz FSB 800mhz

[Don Bowman]

> 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