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SubjectRe: [SCHED] wrong priority calc - SIMPLE test case
At 12:39 PM 1/1/2006 +0100, Paolo Ornati wrote:
>On Sat, 31 Dec 2005 17:37:11 +0100
>Mike Galbraith <efault@gmx.de> 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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