em0, polling performance, P4 2.8ghz FSB 800mhz

[Deepak Jain]

Don Bowman wrote:

>>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).
> 

I'd like to know more about the CPU time idea. I have 
net.inet.udp.blackhole=2 and net.inet.tcp.blackhole=2 because I saw a 
lot of dstunreachable packets out.

The system can hyperthread, but I thought the singlethreading of polling 
might have been an issue, so I recompiled the kernel without SMP.

DJ