src/lib/lttng-ust/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 _LTTNG_GETCPU_H
   8 #define _LTTNG_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 /*
  18  * Initialize the getcpu plugin if it's present.
  19  */
  20 void lttng_ust_getcpu_plugin_init(void)
  21         __attribute__((visibility("hidden")));
  22
  23 /*
  24  * Function pointer to the user provided getcpu callback, can be set at library
  25  * initialization by a dlopened plugin or at runtime by a user by calling
  26  * lttng_ust_getcpu_override() from the public API.
  27  */
  28 extern int (*lttng_ust_get_cpu_sym)(void)
  29         __attribute__((visibility("hidden")));
  30
  31 #ifdef LTTNG_UST_DEBUG_VALGRIND
  32
  33 /*
  34  * Fallback on cpu 0 if liblttng-ust is build with Valgrind support.
  35  * get_cpu() returns the current CPU number. It may change due to
  36  * migration, so it is only statistically accurate.
  37  */
  38 static inline
  39 int lttng_ust_get_cpu_internal(void)
  40 {
  41         return 0;
  42 }
  43
  44 #else
  45
  46 /*
  47  * sched_getcpu.
  48  */
  49 #ifdef __linux__
  50
  51 #if !HAVE_SCHED_GETCPU
  52 #include <sys/syscall.h>
  53 #define __getcpu(cpu, node, cache)      syscall(__NR_getcpu, cpu, node, cache)
  54 /*
  55  * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
  56  */
  57 static inline
  58 int lttng_ust_get_cpu_internal(void)
  59 {
  60         int cpu, ret;
  61
  62         ret = __getcpu(&cpu, NULL, NULL);
  63         if (caa_unlikely(ret < 0))
  64                 return 0;
  65         return cpu;
  66 }
  67 #else /* HAVE_SCHED_GETCPU */
  68 #include <sched.h>
  69
  70 /*
  71  * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
  72  */
  73 static inline
  74 int lttng_ust_get_cpu_internal(void)
  75 {
  76         int cpu;
  77
  78         cpu = sched_getcpu();
  79         if (caa_unlikely(cpu < 0))
  80                 return 0;
  81         return cpu;
  82 }
  83 #endif  /* HAVE_SCHED_GETCPU */
  84
  85 #elif (defined(__FreeBSD__) || defined(__CYGWIN__))
  86
  87 /*
  88  * FreeBSD and Cygwin do not allow query of CPU ID. Always use CPU
  89  * number 0, with the assocated performance degradation on SMP.
  90  */
  91 static inline
  92 int lttng_ust_get_cpu_internal(void)
  93 {
  94         return 0;
  95 }
  96
  97 #else
  98 #error "Please add support for your OS into liblttng-ust/compat.h."
  99 #endif
 100
 101 #endif
 102
 103 static inline
 104 int lttng_ust_get_cpu(void)
 105 {
 106         int (*lttng_ust_get_cpu_current)(void) = CMM_LOAD_SHARED(lttng_ust_get_cpu_sym);
 107
 108         /*
 109          * Fallback to the internal getcpu implementation if no override was
 110          * provided the user.
 111          */
 112         if (caa_likely(!lttng_ust_get_cpu_current)) {
 113                 return lttng_ust_get_cpu_internal();
 114         } else {
 115                 return lttng_ust_get_cpu_current();
 116         }
 117 }
 118
 119 #endif /* _LTTNG_GETCPU_H */