device polling takes more CPU hits??

[Luigi Rizzo]

On Mon, Jul 26, 2004 at 01:18:46PM -0700, Kelly Yancey wrote:
...
>   Out of curiousity, what sort of testing did you do to arrive at these
> settings?  I did some testing a while back with a SmartBits box pumping
> packets through a FreeBSD 2.8Ghz box configured to route between two em
> gigabit interfaces; I found that changing the burst_max and each_burst
> parameters had almost no effect on throughput (maximum 1% difference).

fast boxes are pci-bus limited, not CPU limited(*) so changing the burst
size (which basically amortizes some CPU costs) has little if any
effect.

(*) this doesn't mean that the box cannot livelock, as depending on
the traffic on the bus, the CPU might stall for long intervals
waiting for bus transactions to complete, and becomes unable to
do anything at all. So you might still need polling.

	cheers
	luigi