UDP output performance

[Willem Jan Withagen]

Manish Vachharajani wrote:
> Hmm, what version of FreeBSD are you using?  I don't know the solution
> but I wonder if it is related to a similar problem we are having with
> TCP connection scaling, both under 7.2 and 8.0 over a 10 Gb link.
> We've been trying to track it down, and if you see it for UDP as well
> that may give some clues.
> 
> If you do a netstat -idh what is the output?  Does the recieving
> interface show any Ierrs or drops?  If so, you should be able to do a
> sysctl dev.em.<interface number>.stats=1 and then see some output via
> dmesg.  Does this show any missed packets?
> 
> Oh, also, what kind of machine are you running on?

Well this turns out to be a pilot error, in that I created such a complex 
bandwidth evaluation that on buffer full the packet got tossed in the 
application.
:(

Just stripping that out, and just do a

try send
while(not send) {
	usleep(1 packet-time);
	try again;
}
	
Reduced my packet loss to < 0.1% and I'm able to squeeze a nice > 900 Mbit/s 
  out of a single em(4) port. Still no packets begin dropped in netstat -i.

So now I'm off hunting for 'bugs' in snmp, cacti, mrtg to see why they don't 
like the counters. Even when I'm using the 64bit counters I get really spiky 
  bandwidth results. Equal to those when using 32 bits counters, so 
certainly things are not as I think they are.

Other thing is to see how Lin* is performing on this test.
So trying to install ubuntu 9.04.

--WjW