[lttng-ust.git] / src / common / getcpu.h

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

#ifndef _UST_COMMON_GETCPU_H
#define _UST_COMMON_GETCPU_H

#include <urcu/compiler.h>
#include <urcu/system.h>
#include <urcu/arch.h>

#include <lttng/ust-getcpu.h>

/*
 * Function pointer to the user provided getcpu callback, can be set at library
 * initialization by a dlopened plugin or at runtime by a user by calling
 * lttng_ust_getcpu_override() from the public API.
 *
 * This is an ABI symbol of liblttng-ust-common accessed by other libraries
 * through the static inline function in this file. It is initialised in the
 * liblttng-ust-common constructor.
 */
extern int (*lttng_ust_get_cpu_sym)(void);

#ifdef LTTNG_UST_DEBUG_VALGRIND

/*
 * Fallback on cpu 0 if liblttng-ust is build with Valgrind support.
 * get_cpu() returns the current CPU number. It may change due to
 * migration, so it is only statistically accurate.
 */
static inline
int lttng_ust_get_cpu_internal(void)
{
	return 0;
}

#else

/*
 * sched_getcpu.
 */
#ifdef __linux__

#if !HAVE_SCHED_GETCPU
#include <sys/syscall.h>
#define __getcpu(cpu, node, cache)	syscall(__NR_getcpu, cpu, node, cache)
/*
 * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
 */
static inline
int lttng_ust_get_cpu_internal(void)
{
	int cpu, ret;

	ret = __getcpu(&cpu, NULL, NULL);
	if (caa_unlikely(ret < 0))
		return 0;
	return cpu;
}
#else /* HAVE_SCHED_GETCPU */
#include <sched.h>

/*
 * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
 */
static inline
int lttng_ust_get_cpu_internal(void)
{
	int cpu;

	cpu = sched_getcpu();
	if (caa_unlikely(cpu < 0))
		return 0;
	return cpu;
}
#endif	/* HAVE_SCHED_GETCPU */

#elif (defined(__FreeBSD__) || defined(__CYGWIN__))

/*
 * FreeBSD and Cygwin do not allow query of CPU ID. Always use CPU
 * number 0, with the associated performance degradation on SMP.
 */
static inline
int lttng_ust_get_cpu_internal(void)
{
	return 0;
}

#else
#error "Please add support for your OS into liblttng-ust/compat.h."
#endif

#endif

static inline
int lttng_ust_get_cpu(void)
{
	int (*lttng_ust_get_cpu_current)(void) = CMM_LOAD_SHARED(lttng_ust_get_cpu_sym);

	/*
	 * Fallback to the internal getcpu implementation if no override was
	 * provided the user.
	 */
	if (caa_likely(!lttng_ust_get_cpu_current)) {
		return lttng_ust_get_cpu_internal();
	} else {
		return lttng_ust_get_cpu_current();
	}
}

#endif /* _LTTNG_GETCPU_H */
Commit	Line	Data
	1	/*
	2	* SPDX-License-Identifier: LGPL-2.1-only
	3	*
	4	* Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	5	*/
	6
	7	#ifndef _UST_COMMON_GETCPU_H
	8	#define _UST_COMMON_GETCPU_H
	9
	10	#include <urcu/compiler.h>
	11	#include <urcu/system.h>
	12	#include <urcu/arch.h>
	13
	14	#include <lttng/ust-getcpu.h>
	15
	16	/*
	17	* Function pointer to the user provided getcpu callback, can be set at library
	18	* initialization by a dlopened plugin or at runtime by a user by calling
	19	* lttng_ust_getcpu_override() from the public API.
	20	*
	21	* This is an ABI symbol of liblttng-ust-common accessed by other libraries
	22	* through the static inline function in this file. It is initialised in the
	23	* liblttng-ust-common constructor.
	24	*/
	25	extern int (*lttng_ust_get_cpu_sym)(void);
	26
	27	#ifdef LTTNG_UST_DEBUG_VALGRIND
	28
	29	/*
	30	* Fallback on cpu 0 if liblttng-ust is build with Valgrind support.
	31	* get_cpu() returns the current CPU number. It may change due to
	32	* migration, so it is only statistically accurate.
	33	*/
	34	static inline
	35	int lttng_ust_get_cpu_internal(void)
	36	{
	37	return 0;
	38	}
	39
	40	#else
	41
	42	/*
	43	* sched_getcpu.
	44	*/
	45	#ifdef __linux__
	46
	47	#if !HAVE_SCHED_GETCPU
	48	#include <sys/syscall.h>
	49	#define __getcpu(cpu, node, cache) syscall(__NR_getcpu, cpu, node, cache)
	50	/*
	51	* If getcpu is not implemented in the kernel, use cpu 0 as fallback.
	52	*/
	53	static inline
	54	int lttng_ust_get_cpu_internal(void)
	55	{
	56	int cpu, ret;
	57
	58	ret = __getcpu(&cpu, NULL, NULL);
	59	if (caa_unlikely(ret < 0))
	60	return 0;
	61	return cpu;
	62	}
	63	#else /* HAVE_SCHED_GETCPU */
	64	#include <sched.h>
	65
	66	/*
	67	* If getcpu is not implemented in the kernel, use cpu 0 as fallback.
	68	*/
	69	static inline
	70	int lttng_ust_get_cpu_internal(void)
	71	{
	72	int cpu;
	73
	74	cpu = sched_getcpu();
	75	if (caa_unlikely(cpu < 0))
	76	return 0;
	77	return cpu;
	78	}
	79	#endif /* HAVE_SCHED_GETCPU */
	80
	81	#elif (defined(__FreeBSD__) \|\| defined(__CYGWIN__))
	82
	83	/*
	84	* FreeBSD and Cygwin do not allow query of CPU ID. Always use CPU
	85	* number 0, with the associated performance degradation on SMP.
	86	*/
	87	static inline
	88	int lttng_ust_get_cpu_internal(void)
	89	{
	90	return 0;
	91	}
	92
	93	#else
	94	#error "Please add support for your OS into liblttng-ust/compat.h."
	95	#endif
	96
	97	#endif
	98
	99	static inline
	100	int lttng_ust_get_cpu(void)
	101	{
	102	int (*lttng_ust_get_cpu_current)(void) = CMM_LOAD_SHARED(lttng_ust_get_cpu_sym);
	103
	104	/*
	105	* Fallback to the internal getcpu implementation if no override was
	106	* provided the user.
	107	*/
	108	if (caa_likely(!lttng_ust_get_cpu_current)) {
	109	return lttng_ust_get_cpu_internal();
	110	} else {
	111	return lttng_ust_get_cpu_current();
	112	}
	113	}
	114
	115	#endif /* _LTTNG_GETCPU_H */