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Date: Mon, 26 Nov 2001 12:49:47 -0800 (PST)
From: Davide Libenzi <davidel@xmailserver.org>
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To: Mike Kravetz <kravetz@us.ibm.com>
cc: lkml <linux-kernel@vger.kernel.org>
Subject: Re: Scheduler Cleanup
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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



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