reschedule_idle changes in ac kernels

[Mike Kravetz]

I just noticed the changes to reschedule_idle() in the 2.4.5-ac
kernel.  I suspect these are the changes made for:

o       Fix off by one on real time pre-emption in scheduler

I'm curious if anyone has ran any benchmarks before and after
applying this fix.

The reason I ask is that during the development of my multi-queue
scheduler, I 'accidently' changed reschedule_idle code to trigger
a preemption if preemption_goodness() was greater than 0, as
opposed to greater than 1.  I believe this is the same change made
to the ac kernel.  After this change, we saw a noticeable drop in
performance for some benchmarks.

The drop in performance I saw could have been the result of a
combination of the change, and my multi-queue scheduler.  However,
in any case aren't we now going to trigger more preemptions?

I understand that we need to make the fig to get the realtime
semantics correct,  but we also need to be aware of performance in
the non-realtime case.

-- 
Mike Kravetz                                 [e-mail]
IBM Linux Technology Center