Ingo Molnar wrote:
> this was done intentionally, and this scenario (1+2 tasks) is the very
> worst scenario. The problem is that by trying to balance all 3 tasks we
> now have 3 tasks that trash their cache going from one CPU to another.  
> (this is what happens with your patch - even with another approach we'd
> have to trash at least one task)
> 
> By keeping 2 tasks on one CPU and 1 task on the other CPU we avoid
> cross-CPU migration of threads. Think about the 2+3 or 4+5 tasks case
> rather, do we want absolutely perfect balancing, or good SMP affinity and
> good combined performance?
OK...  But what about the (imbalance / 2) part?  Either the comment 
needs to change, or the code.  Attatched is a slightly revised patch for 
the code.  The comment patch would be even easier:

- 
/* It needs an at least ~25% imbalance to trigger balancing. */
+ 
/* It needs an at least ~50% imbalance to trigger balancing. */

Either way works for me.  I'd like to see something done, as the 
comments don't match the code right now...

Cheers!

-Matt