linux-kernel - Re: [PATCH] sched: fix RLIMIT_RTTIME when PI-boosting to RT

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Message-ID: <20150310054252.GA11485@gmail.com>
Date:	Tue, 10 Mar 2015 06:42:52 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Brian Silverman <brian@...oton-tech.com>
Cc:	mingo <mingo@...hat.com>, peterz <peterz@...radead.org>,
	Austin Schuh <austin@...oton-tech.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH] sched: fix RLIMIT_RTTIME when PI-boosting to RT


* Brian Silverman <brian@...oton-tech.com> wrote:

> 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.

Mind sending a patch that sticks this testcase into 
tools/testing/selftests/sched/ or so, with the new 'sched' directory 
and new Makefile to be created by you as well?

I've reformatted the testcase below, to kernel coding style. Note that 
I added a minimal license notification, you might want to add your 
copyright.

Thanks,

	Ingo

==========================>


/*
 * RLIMIT_RTTIME test code. Compile with:
 *
 *     gcc -pthread -lrt test_pi.c
 *
 * It requires permission to set a realtime scheduling policy of 2 when running.
 *
 * License: GPLv2
 */
#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(&param, 0, sizeof(param));
	param.sched_priority = 2;
	assert(sched_setscheduler(0, SCHED_FIFO, &param) == 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;
}
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