Although still insufficient in certain cases. All flows are not equal; as an
example, an IPSEC flow with 1000 packets bound to one CPU  will likely
utilize more cycles than 5000 packets that are being plain forwarded on
another CPU.

sure; however the kernel doesn't provide more accurate information
currently (and I doubt it could even, it's not so easy to figure out
which interface triggered the softirq if 2 interfaces share the cpu, and
then, how much work came from which etc).

also the "amount of work" estimate doesn't need to be accurate to 5
digits to be honest... just number of packets seems to be a quite
reasonable approximation already. (if the kernel starts exporting more
accurate data, irqbalance can easily use it of course)
-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org