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

[Mike Galbraith]

At 12:39 PM 1/1/2006 +0100, Paolo Ornati wrote:
> On Sat, 31 Dec 2005 17:37:11 +0100
> Mike Galbraith <efault@xxxxxx> wrote:
>
> > Strange.  Using the exact same arguments, I do see some odd bouncing up to
> > high priorities, but they spend the vast majority of their time down at 25.
>
> Mmmm... to make it more easly reproducible I've enlarged the sleep time
> (1 microsecond is likely to be rounded too much and give different
> results on different hardware/kernel/config...).
>
> Compile this _without_ optimizations and try again:

<snip>

> Try different values: 1000, 2000, 3000 ... are you able to reproduce it
> now?

Yeah.  One instance running has to sustain roughly _95%_ cpu before it's 
classified as a cpu piggy.  Not good.

> If yes, try to start 2 of them with something like this:
>
> "./a.out 3000 & ./a.out 3161"
>
> so they are NOT syncronized and they use almost all the CPU time:
>
>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>  5582 paolo     16   0  2396  320  252 S 45.7  0.1   0:05.52 a.out
>  5583 paolo     15   0  2392  320  252 S 45.7  0.1   0:05.49 a.out
>
> This is the bad situation I hate: some cpu-eaters that eat all the CPU
> time BUT have a really good priority only because they sleeps a bit.

Yup, your proggy fools the interactivity estimator quite well.  This 
problem was addressed a long time ago, and thought to be more or less 
cured.  Guess not.

        -Mike 

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