[lttng-ust.git] / src / common / smp.c

/*
 * SPDX-License-Identifier: LGPL-2.1-only
 *
 * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
 */

#define _LGPL_SOURCE
#include <unistd.h>
#include <pthread.h>

#include <urcu/compiler.h>

#include "common/smp.h"

static int num_possible_cpus_cache;

#if (defined(__GLIBC__) || defined( __UCLIBC__))
static void _get_num_possible_cpus(void)
{
	int result;

	/* On Linux, when some processors are offline
	 * _SC_NPROCESSORS_CONF counts the offline
	 * processors, whereas _SC_NPROCESSORS_ONLN
	 * does not. If we used _SC_NPROCESSORS_ONLN,
	 * getcpu() could return a value greater than
	 * this sysconf, in which case the arrays
	 * indexed by processor would overflow.
	 */
	result = sysconf(_SC_NPROCESSORS_CONF);
	if (result == -1)
		return;
	num_possible_cpus_cache = result;
}

#else

/*
 * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not
 * return the number of configured CPUs in the system but relies on the cpu
 * affinity mask of the current task.
 *
 * So instead we use a strategy similar to GLIBC's, counting the cpu
 * directories in "/sys/devices/system/cpu" and fallback on the value from
 * sysconf if it fails.
 */

#include <dirent.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>

#define __max(a,b) ((a)>(b)?(a):(b))

static void _get_num_possible_cpus(void)
{
	int result, count = 0;
	DIR *cpudir;
	struct dirent *entry;

	cpudir = opendir("/sys/devices/system/cpu");
	if (cpudir == NULL)
		goto end;

	/*
	 * Count the number of directories named "cpu" followed by and
	 * integer. This is the same strategy as glibc uses.
	 */
	while ((entry = readdir(cpudir))) {
		if (entry->d_type == DT_DIR &&
			strncmp(entry->d_name, "cpu", 3) == 0) {

			char *endptr;
			unsigned long cpu_num;

			cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
			if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
					&& (*endptr == '\0')) {
				count++;
			}
		}
	}

end:
	/*
	 * Get the sysconf value as a fallback. Keep the highest number.
	 */
	result = __max(sysconf(_SC_NPROCESSORS_CONF), count);

	/*
	 * If both methods failed, don't store the value.
	 */
	if (result < 1)
		return;
	num_possible_cpus_cache = result;
}
#endif

/*
 * Returns the total number of CPUs in the system. If the cache is not yet
 * initialized, get the value from the system through sysconf and cache it.
 *
 * If the sysconf call fails, don't populate the cache and return 0.
 */
int num_possible_cpus(void)
{
	if (caa_unlikely(!num_possible_cpus_cache))
		_get_num_possible_cpus();

	return num_possible_cpus_cache;
}
Commit	Line	Data
ebabbf58	1	/*
c0c0989a	2	* SPDX-License-Identifier: LGPL-2.1-only
ebabbf58 MD	3	*
	4	* Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	5	* Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
ebabbf58 MD	6	*/
ebabbf58 MD	7
ebabbf58 MD	8	#define _LGPL_SOURCE
	9	#include <unistd.h>
	10	#include <pthread.h>
ebabbf58	11
74cc1f59 MJ	12	#include <urcu/compiler.h>
	13
	14	#include "common/smp.h"
	15
	16	static int num_possible_cpus_cache;
ebabbf58 MD	17
ebabbf58 MD	18	#if (defined(__GLIBC__) \|\| defined( __UCLIBC__))
74cc1f59	19	static void _get_num_possible_cpus(void)
ebabbf58 MD	20	{
	21	int result;
	22
	23	/* On Linux, when some processors are offline
	24	* _SC_NPROCESSORS_CONF counts the offline
	25	* processors, whereas _SC_NPROCESSORS_ONLN
	26	* does not. If we used _SC_NPROCESSORS_ONLN,
	27	* getcpu() could return a value greater than
	28	* this sysconf, in which case the arrays
	29	* indexed by processor would overflow.
	30	*/
	31	result = sysconf(_SC_NPROCESSORS_CONF);
	32	if (result == -1)
	33	return;
74cc1f59	34	num_possible_cpus_cache = result;
ebabbf58 MD	35	}
	36
	37	#else
	38
	39	/*
	40	* The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not
	41	* return the number of configured CPUs in the system but relies on the cpu
	42	* affinity mask of the current task.
	43	*
	44	* So instead we use a strategy similar to GLIBC's, counting the cpu
	45	* directories in "/sys/devices/system/cpu" and fallback on the value from
	46	* sysconf if it fails.
	47	*/
	48
	49	#include <dirent.h>
	50	#include <limits.h>
	51	#include <stdlib.h>
	52	#include <string.h>
	53	#include <sys/types.h>
	54
	55	#define __max(a,b) ((a)>(b)?(a):(b))
	56
74cc1f59	57	static void _get_num_possible_cpus(void)
ebabbf58 MD	58	{
	59	int result, count = 0;
	60	DIR *cpudir;
	61	struct dirent *entry;
	62
	63	cpudir = opendir("/sys/devices/system/cpu");
	64	if (cpudir == NULL)
	65	goto end;
	66
	67	/*
	68	* Count the number of directories named "cpu" followed by and
	69	* integer. This is the same strategy as glibc uses.
	70	*/
	71	while ((entry = readdir(cpudir))) {
	72	if (entry->d_type == DT_DIR &&
	73	strncmp(entry->d_name, "cpu", 3) == 0) {
	74
	75	char *endptr;
	76	unsigned long cpu_num;
	77
	78	cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
	79	if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
	80	&& (*endptr == '\0')) {
	81	count++;
	82	}
	83	}
	84	}
	85
	86	end:
	87	/*
	88	* Get the sysconf value as a fallback. Keep the highest number.
	89	*/
	90	result = __max(sysconf(_SC_NPROCESSORS_CONF), count);
	91
	92	/*
	93	* If both methods failed, don't store the value.
	94	*/
	95	if (result < 1)
	96	return;
74cc1f59	97	num_possible_cpus_cache = result;
ebabbf58 MD	98	}
ebabbf58 MD	99	#endif
74cc1f59 MJ	100
	101	/*
	102	* Returns the total number of CPUs in the system. If the cache is not yet
	103	* initialized, get the value from the system through sysconf and cache it.
	104	*
	105	* If the sysconf call fails, don't populate the cache and return 0.
	106	*/
	107	int num_possible_cpus(void)
	108	{
	109	if (caa_unlikely(!num_possible_cpus_cache))
	110	_get_num_possible_cpus();
	111
	112	return num_possible_cpus_cache;
	113	}