Re: [SCHED] wrong priority calc - SIMPLE test case

[Mike Galbraith]

At 02:52 PM 12/30/2005 +0100, Paolo Ornati wrote:
> WAS: [SCHED] Totally WRONG prority calculation with specific test-case
> (since 2.6.10-bk12)
> http://lkml.org/lkml/2005/12/27/114/index.html
>
> On Wed, 28 Dec 2005 10:26:58 +1100
> Con Kolivas <kernel@xxxxxxxxxxx> wrote:
>
> > The issue is that the scheduler interactivity estimator is a state 
> machine and
> > can be fooled to some degree, and a cpu intensive task that just 
> happens to
> > sleep a little bit gets significantly better priority than one that is 
> fully
> > cpu bound all the time. Reverting that change is not a solution because it
> > can still be fooled by the same process sleeping lots for a few seconds 
> or so
> > at startup and then changing to the cpu mostly-sleeping slightly 
> behaviour.
> > This "fluctuating" behaviour is in my opinion worse which is why I removed
> > it.
>
> Trying to find a "as simple as possible" test case for this problem
> (that I consider a BUG in priority calculation) I've come up with this
> very simple program:
>
> ------ sched_fooler.c -------------------------------

Ingo seems to have done something in 2.6.15-rc7-rt1 which defeats your 
little proggy.  Taking a quick peek at the rt scheduler changes, nothing 
poked me in the eye, but by golly, I can't get this kernel to act up, 
whereas 2.6.14-virgin does.

        -Mike  (off to stare harder rt patch) 

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