asymmetric smp

[Matt Thomas <matt%3am-software.com@localhost>]

I recently ordered an ODROID-XU Lite to help beat on the my ARM MP code.

However, it has a quirk that I don't think our scheduler will deal with.

It has 4 Cortex-A15 cores @ 1.4Ghz and 4 Cortex-A7 cores @ 1.2Ghz.  Even if the 
frequencies weren't different, the A15 cores at least twice as fast per cycle 
than the A7.  That asymmetry is going to cause havoc with the scheduler.  In 
terms of power, the A7s use a lot less than the A15s so if you can keep the 
work on the A7s and leave the A15s sleeping, you'll extend your battery life a 
lot.

It should also be noted the A15s have different cache structure than the A7s as 
well.

There is no hyperthreading so that headache.

Imagine doing a build, you might want to keep the shells and the like on the A7 
while letting A15s get the compiler/assembler/loader (more compute intensive).