From: Brian Silverman <brian@peloton-tech.com>
To: mingo <mingo@redhat.com>, peterz <peterz@infradead.org>
Cc: Austin Schuh <austin@peloton-tech.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Brian Silverman <brian@peloton-tech.com>
Subject: Re: [PATCH] sched: fix RLIMIT_RTTIME when PI-boosting to RT
Date: Wed, 18 Feb 2015 19:23:12 -0500 [thread overview]
Message-ID: <CAGt3f4=HmWU0ng=PNNyzA_5-FefMmWg-pOKzSL3Sc0ow=xHVug@mail.gmail.com> (raw)
In-Reply-To: <1424305436-6716-1-git-send-email-brian@peloton-tech.com>
Here's my test code. Compile with `gcc -pthread -lrt test_pi.c`. It
requires permission to set a realtime scheduling policy of 2 when
running.
#define _GNU_SOURCE
#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <time.h>
#include <sched.h>
#include <assert.h>
#include <sys/resource.h>
#include <string.h>
#include <signal.h>
#include <stdlib.h>
static const struct timespec kSleepTime = {0, 10000};
static pthread_mutex_t mutex;
extern void nop() {}
void *nonrealtime(void *ignored_param) {
while (1) {
assert(pthread_mutex_lock(&mutex) == 0);
assert(pthread_mutex_unlock(&mutex) == 0);
assert(clock_nanosleep(CLOCK_MONOTONIC, 0, &kSleepTime, NULL) == 0);
}
}
void *realtime(void *ignored_param) {
struct sched_param param;
memset(¶m, 0, sizeof(param));
param.sched_priority = 2;
assert(sched_setscheduler(0, SCHED_FIFO, ¶m) == 0);
while (1) {
assert(pthread_mutex_lock(&mutex) == 0);
assert(clock_nanosleep(CLOCK_MONOTONIC, 0, &kSleepTime, NULL) == 0);
assert(pthread_mutex_unlock(&mutex) == 0);
}
}
void signal_handler(int number) {
printf("got signal %d, SIGXCPU=%d\n", number, SIGXCPU);
exit(0);
}
int main() {
struct sigaction action;
memset(&action, 0, sizeof(action));
action.sa_handler = signal_handler;
assert(sigaction(SIGXCPU, &action, NULL) == 0);
struct rlimit rlim;
rlim.rlim_cur = 500;
rlim.rlim_max = 5000;
assert(prlimit(0, RLIMIT_RTTIME, &rlim, NULL) == 0);
pthread_mutexattr_t mutexattr;
assert(pthread_mutexattr_init(&mutexattr) == 0);
assert(pthread_mutexattr_setprotocol(&mutexattr, PTHREAD_PRIO_INHERIT) == 0);
assert(pthread_mutex_init(&mutex, &mutexattr) == 0);
assert(pthread_mutexattr_destroy(&mutexattr) == 0);
pthread_t nrt, rt;
assert(pthread_create(&nrt, NULL, nonrealtime, NULL) == 0);
assert(pthread_create(&rt, NULL, realtime, NULL) == 0);
assert(pthread_join(nrt, NULL) == 0);
assert(pthread_join(rt, NULL) == 0);
return 0;
}
On Wed, Feb 18, 2015 at 7:23 PM, <brian@peloton-tech.com> wrote:
> From: Brian Silverman <brian@peloton-tech.com>
>
> When non-realtime tasks get priority-inheritance boosted to a realtime
> scheduling class, RLIMIT_RTTIME starts to apply to them. However, the
> counter used for checking this (the same one used for SCHED_RR
> timeslices) was not getting reset. This meant that tasks running with a
> non-realtime scheduling class which are repeatedly boosted to a realtime
> one, but never block while they are running realtime, eventually hit the
> timeout without ever running for a time over the limit. This patch
> resets the realtime timeslice counter when un-PI-boosting from an RT to
> a non-RT scheduling class.
>
> I have some test code with two threads and a shared PTHREAD_PRIO_INHERIT
> mutex which induces priority boosting and spins while boosted that gets
> killed by a SIGXCPU on non-fixed kernels but doesn't with this patch
> applied. It happens much faster with a CONFIG_PREEMPT_RT kernel, and
> does happen eventually with PREEMPT_VOLUNTARY kernels.
>
> Signed-off-by: Brian Silverman <brian@peloton-tech.com>
> ---
> I am not subscribed to the list so please CC me on any responses.
>
> kernel/sched/core.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 87b9814..16ad0ed 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3192,6 +3192,8 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
> } else {
> if (dl_prio(oldprio))
> p->dl.dl_boosted = 0;
> + if (rt_prio(oldprio))
> + p->rt.timeout = 0;
> p->sched_class = &fair_sched_class;
> }
>
> --
> 1.7.10.4
>
next prev parent reply other threads:[~2015-02-19 0:23 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-19 0:23 [PATCH] sched: fix RLIMIT_RTTIME when PI-boosting to RT brian
2015-02-19 0:23 ` Brian Silverman [this message]
2015-03-10 5:42 ` Ingo Molnar
2015-03-05 17:10 ` Austin Schuh
2015-03-09 17:34 ` Sebastian Andrzej Siewior
2015-03-09 23:29 ` Brian Silverman
2015-03-23 12:24 ` [tip:sched/core] sched: Fix " tip-bot for Brian Silverman
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