On 1/23/06, Adam Gibson <agibson at ptm dot com> wrote:
> I was pushing about 5.5 MBytes/sec through a 400mhz Axiomtek NA-0041B
> (comes with 4 built-in realtek/rtl nics) and noticed that CPU usage was
> at 73%. This is without any VPN overhead. Traffic was passing from LAN
> to OPT1. I then enabled device polling and CPU usage went down to 0% -
> 1% during the same transfers.
It typically gets you as much as 50% higher throughput, at the cost of
slightly increased latency. The CPU numbers with polling are
deceiving because it doesn't take the CPU time spent on polling into
account on FreeBSD 4.x.
> I was rather surprised that a 400mhz system is barely able to keep up
> with 5.5MBytes/sec without device polling since that is the default.
5.5 MBps is about 44 Mbps, so you could probably squeeze ~50-60 Mbps
through that box without polling. That's actually quite good for
Realtek NIC's with a 400 MHz.
See 2.5.2 and 2.5.3: