/*
 * Copyright (C) 2013-2021 Canonical, Ltd.
 * Copyright (C)      2022 Colin Ian King.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 */
#include "stress-ng.h"

static const stress_help_t help[] = {
	{ "y N", "yield N",	"start N workers doing sched_yield() calls" },
	{ NULL,	 "yield-ops N",	"stop after N bogo yield operations" },
	{ NULL,	 NULL,		NULL }
};

#if defined(_POSIX_PRIORITY_SCHEDULING) &&	\
    !defined(__minix__)

/*
 *  stress on sched_yield()
 *	stress system by sched_yield
 */
static int stress_yield(const stress_args_t *args)
{
	uint64_t *counters;
	uint64_t max_ops_per_yielder;
	size_t counters_sz;
	int32_t cpus = stress_get_processors_configured();
	const uint32_t instances = args->num_instances;
	uint32_t yielders = 2;
#if defined(HAVE_SCHED_GETAFFINITY)
	cpu_set_t mask;
#endif
	pid_t *pids;
	size_t i;

#if defined(HAVE_SCHED_GETAFFINITY)
	/*
	 *  If the process is limited to a subset of cores
	 *  then make sure we do not create too many yielders
	 */
	if (sched_getaffinity(0, sizeof(mask), &mask) < 0) {
		pr_inf("%s: can't get sched affinity, defaulting to %"
			PRId32 " yielder%s (instance %" PRIu32 ")\n",
			args->name, cpus, (cpus == 1) ? "" : "s", args->instance);
	} else {
		if (CPU_COUNT(&mask) < (int)cpus)
			cpus = (int32_t)CPU_COUNT(&mask);
		pr_inf("%s: limiting to %" PRId32 " child yielder%s (instance %"
			PRIu32 ")\n", args->name, cpus, (cpus == 1) ? "" : "s", args->instance);
	}
#else
	UNEXPECTED
#endif

	/*
	 *  Ensure we always have at least 2 yielders per
	 *  CPU available to force context switching on yields
	 */
	if (cpus > 0) {
		cpus *= 2;
		yielders = cpus / instances;
		if (yielders < 1)
			yielders = 1;
		if (!args->instance) {
			/* residual may be -ve, ensure it is signed */
			int32_t residual = cpus - (int32_t)(yielders * instances);

			if (residual > 0)
				yielders += residual;
		}
	}

	max_ops_per_yielder = args->max_ops / yielders;
	pids = calloc(yielders, sizeof(*pids));
	if (!pids) {
		pr_err("%s: calloc failed\n", args->name);
		return EXIT_NO_RESOURCE;
	}

	counters_sz = yielders * sizeof(*counters);
	counters = (uint64_t *)mmap(NULL, counters_sz, PROT_READ | PROT_WRITE,
		MAP_SHARED | MAP_ANONYMOUS, -1, 0);
	if (counters == MAP_FAILED) {
		int rc = stress_exit_status(errno);

		pr_err("%s: mmap failed: errno=%d (%s)\n",
			args->name, errno, strerror(errno));
		free(pids);
		return rc;
	}
	(void)memset(counters, 0, counters_sz);

	stress_set_proc_state(args->name, STRESS_STATE_RUN);

	for (i = 0; keep_stressing_flag() && (i < yielders); i++) {
		pids[i] = fork();
		if (pids[i] < 0) {
			pr_dbg("%s: fork failed (instance %" PRIu32
				", yielder %zd): errno=%d (%s)\n",
				args->name, args->instance, i, errno, strerror(errno));
		} else if (pids[i] == 0) {
			stress_parent_died_alarm();
			(void)sched_settings_apply(true);

			do {
				int ret;

				ret = shim_sched_yield();
				if ((ret < 0) && (g_opt_flags & OPT_FLAGS_VERIFY))
					pr_fail("%s: sched_yield failed, errno=%d (%s)\n",
						args->name, errno, strerror(errno));
				counters[i]++;
			} while (keep_stressing_flag() && (!max_ops_per_yielder || (counters[i] < max_ops_per_yielder)));
			_exit(EXIT_SUCCESS);
		}
	}

	do {
		set_counter(args, 0);
#if defined(__FreeBSD__)
		VOID_RET(int, shim_sched_yield());
#else
		VOID_RET(int, shim_usleep(100000));
#endif

		for (i = 0; i < yielders; i++)
			add_counter(args, counters[i]);
	} while (keep_stressing(args));

	/* Parent, wait for children */
	set_counter(args, 0);

	stress_set_proc_state(args->name, STRESS_STATE_DEINIT);
	for (i = 0; i < yielders; i++) {
		if (pids[i] > 0) {
			int status;

			(void)kill(pids[i], SIGKILL);
			(void)shim_waitpid(pids[i], &status, 0);
			add_counter(args, counters[i]);
		}
	}
	(void)munmap((void *)counters, counters_sz);
	free(pids);

	return EXIT_SUCCESS;
}

stressor_info_t stress_yield_info = {
	.stressor = stress_yield,
	.class = CLASS_SCHEDULER | CLASS_OS,
	.verify = VERIFY_OPTIONAL,
	.help = help
};
#else
stressor_info_t stress_yield_info = {
	.stressor = stress_not_implemented,
	.class = CLASS_SCHEDULER | CLASS_OS,
	.help = help
};
#endif
