Re: Scheduler Cleanup

[Davide Libenzi]

On Mon, 26 Nov 2001, Mike Kravetz wrote:

> I'm happy to see the cleanup of scheduler code that went into
> 2.4.15/16.  One small difference in behavior (I think) is that
> the currently running task is not given preference over other
> tasks on the runqueue with the same 'goodness' value.  I would
> think giving the current task preference is a good thing
> (especially in light of recent discussions about too frequent
> moving/rescheduling of tasks).  Can someone provide the rational
> for this change?  Was it just the result of making the code
> cleaner?  Is it believed that this won't really make a difference?

Mike, I was actually surprised about the presence of that check inside the
previous code.
If you think about it, when a running task is scheduled ?

1) an IRQ wakeup some I/O bound task
2) the quota is expired

With 1) you've an incoming I/O bound task ( ie: ksoftirqd_* ) that is very
likely going to have a better dynamic priority ( if not reschedule_idle()
does not set need_resched ), while with 2) you've the task counter == 0.
In both cases not only the test is useless but is going to introduce 1)
the branch in the fast path 2) the cost of an extra goodness().

- Davide