src/common/getcpu.h

   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 assocated 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 */