Device polling, kern.polling.burst_max and gig-e

[Steve Francis]

We have a 4.9-RELEASE-p1 box dedicated to some traffic analysis.   It 
monitors on two em interfaces: about 200,000 pps on one interface, and 
180,000 pps on the other.
It's been dealing with that OK, but our traffic levels are increasing - 
we reached over 240,000 pps on one interface last week. This made CPU 
reach 100%, and some packets not get processed.
So, last night we enabled polling on the nics.
Initially, great result - CPU dropped from 82% load (45% system load due 
to interupts) yesterday to 55% load today (12% in system), for same pps 
load (about 300,000 pps total) at the time.

However, input errors went from 0 to about 1200 (oddly, it was 1200 
every other second, and 0 for the seconds in-between.)

A bit of digging around led me to increase kern.polling.burst_max.
According to http://info.iet.unipi.it/~luigi/polling/, "The default 
value is enough for a 100Mbit ethernet".  I increased it gradually to 
900, whcih has almost (but not entirely) eliminated the errors. Now the 
errors are zero for most intervals, but every 10 or so intervals there 
are between 10 and 100 input errors.

So:
- does it make sense to leave the default at 150, in this day of gigabit 
nics?
- is there a danger in increasing the burt_max?  (My burst size goes 
straight to the max of 900.)
- can it be increased more ?
-  are there other variables that make sense to increase for gigabit? 
(like kern.polling.each_burst:?)

Since I increased the burst max, I now have slowly incrementing 
kern.polling.lost_polls - about 1 every 2 seconds. Anything to worry about?

Thanks
Steve Francis