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

Al Boldi
2007-05-03T06:38:58Z

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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;
}