Messages in this thread | | | Date | Sat, 30 Jun 2007 23:06:49 +0200 | From | Willy Tarreau <> | Subject | Re: [patch] CFS scheduler, -v18 |
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Ingo,
I've accidentally discovered a problem with -v18.
Some time ago, I wrote a small program to prevent my laptop from entering low-power mode, and noticed that after upgrading my laptop's kernel from 2.4.20.9+cfs-v6 to 2.4.20.14+cfs-v18, it completely freezes if I run this program.
The program is trivial, it just sets its prio to nice +20 and forks a busy loop. I've added the ability to stop the loop after a user-definable number of iterations, and I can confirm that it unfreezes when the loop ends. I'm not even root when I run it.
Everything freezes, including the frame-buffer. It's not 100% reproducible, I would say 90% only. Sometimes it requires a few seconds before freezing. It *seems* to me that running another task in parallel (such as vmstat) increases its chances to freeze. It seems like nicing to +19 does not cause any trouble.
I've tried it on my dual athlon, and with 1 process I see occasional pauses of 1 or 2 seconds, and with 2 processes, I see fairly larger pauses.
Here's the trivial program. Probably you'll find an obvious bug.
Regards, Willy
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/* * cfs-freeze.c * Fork a busy loop running with idle prio. This often results * in complete freezes with CFS-v18. * * $ gcc -O2 -s -o cfs-freeze cfs-freeze.c * $ ./cfs-freeze */
#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sched.h> #include <sys/time.h> #include <sys/resource.h>
int main(int argc, char **argv) { struct sched_param sch; long long i;
if (argc > 1) i = atoll(argv[1]);
if (i <= 0) i = 4 * 1000 * 1000 * 1000ULL;
sch.sched_priority = 0; sched_setscheduler(0, SCHED_OTHER, &sch); setpriority(PRIO_PROCESS, 0, 20); if (fork() == 0) while (i--); return 0; }
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