linux-kernel - Re: SD scheduler testing hitch

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Message-Id: <1175966255.11408.5.camel@Homer.simpson.net>
Date:	Sat, 07 Apr 2007 19:17:35 +0200
From:	Mike Galbraith <efault@....de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Con Kolivas <kernel@...ivas.org>
Subject: Re: SD scheduler testing hitch

On Sat, 2007-04-07 at 18:20 +0200, Mike Galbraith wrote:

> xx.c
> 
> #include <stdio.h>
> #include <sys/time.h>
> 
> #define max(a,b) ((a) > (b) ? (a) : (b))
> #define min(a,b) ((a) < (b) ? (a) : (b))
> 
> int main(void)
> {
>     struct timeval then, now;
>     struct timespec t = {0, 1000}, r;
> 
>     for(;;) {
>         int t1, t2;
>         short i;
> 
>         if (gettimeofday(&then, 0))
>             break;
>         for (i = 1; i > 0; i++);
>         if (gettimeofday(&now, 0))
>             break;
>         t2 = max(then.tv_usec, now.tv_usec);
>         t1 = min(then.tv_usec, now.tv_usec);
>         if (t2 - t1 >= 1000 && nanosleep(&t, &r))
>             break;
>     }
>     return 0;
> }

I lowered the time to 500us, and ran at nice -10.. it starves tenpercent
here every time.  (ran as taskset -c 1 nice -n -10 ./fairtest)  The
starving 10% duty cycle task has trouble getting 1% CPU.

	-Mike

View attachment "fairtest.c" of type "text/x-csrc" (4378 bytes)