Re: [ck] [REPORT] 2.6.21.1 vs 2.6.21-sd046 vs 2.6.21-cfs-v6

[Al Boldi <a1426z@gawab.com>]

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William Lee Irwin III wrote:
> William Lee Irwin III wrote:
> >> That's odd. The ->load_weight changes should've improved that quite
> >> a bit. There may be something slightly off in how lag is computed,
> >> or maybe the O(n) lag issue Ying Tang spotted is biting you.
>
> On Thu, May 03, 2007 at 06:51:43AM +0300, Al Boldi wrote:
> > Is it not biting you too?
>
> I'm a kernel programmer. I'm not an objective tester.
>
> It also happens to be the case that I personally have never encountered
> a performance problem with any of the schedulers, mainline included, on
> any system I use interactively. So my "user experience" is not valuable.
>
> William Lee Irwin III wrote:
> >> Also, I should say that the nice number affairs don't imply fairness
> >> per se. The way that works is that when tasks have "weights" (like
> >> nice levels in UNIX) the definition of fairness changes so that each
> >> task gets shares of CPU bandwidth proportional to its weight instead
> >> of one share for one task.
>
> On Thu, May 03, 2007 at 06:51:43AM +0300, Al Boldi wrote:
> > Ok, but you can easily expose scheduler unfairness by using nice levels
> > as relative magnifiers; provided nice levels are implemented correctly.
>
> This doesn't really fit in with anything I'm aware of.

You are not the first person that doesn't understand what I'm talking about.  
Don't worry about it.

> William Lee Irwin III wrote:
> >> The other thing to do is try a different number of tasks with a
> >> different mix of nice levels. The weight w_i for a given nice
> >> level n_i should be the same even in a different mix of tasks
> >> and nice levels if the nice levels are the same.
> >> If this sounds too far out, there's nothing to worry about. You can
> >> just run the different numbers of tasks with different mixes of nice
> >> levels and post the %cpu numbers. Or if that's still a bit far out
> >> for you, a test that does all this is eventually going to get written.
>
> On Thu, May 03, 2007 at 06:51:43AM +0300, Al Boldi wrote:
> > chew.c does exactly that, just make sure sched_granularity_ms >=
> > 5,000,000.
>
> Please post the source of chew.c

Attached.


Thanks!

--
Al



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/*
 * original idea by Chris Friesen.  Thanks.
 */

#include <stdio.h>
#include <sys/time.h>
#include <sys/resource.h>

#define THRESHOLD_USEC 2000

unsigned long long stamp()
{
        struct timeval tv;
        gettimeofday(&tv, 0);
        return (unsigned long long) tv.tv_usec + ((unsigned long long) tv.tv_sec)*1000000;
}


int main()
{
        unsigned long long thresh_ticks = THRESHOLD_USEC;
        unsigned long long cur, last, start, act, delta;
        struct timespec ts;

        sched_rr_get_interval(0, &ts);
        printf("pid %d, prio %3d, interval of %d nsec\n", getpid(), getpriority(PRIO_PROCESS, 0), ts.tv_nsec);

        start = last = stamp();
        while(1) {
                cur = stamp();
                delta = cur-last;
                if (delta > thresh_ticks) {
			act = last - start;
                        printf("pid %d, prio %3d, out for %4llu ms, ran for %4llu ms, load %3llu%\n"
			, getpid(), getpriority(PRIO_PROCESS, 0), delta/1000, act/1000,(act*100)/(cur-start));
                        start = cur = stamp();
                }
                last = cur;
        }

        return 0;
}