src/libringbuffer/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 void lttng_ust_getcpu_init(void)
  15         __attribute__((visibility("hidden")));
  16
  17 extern int (*lttng_get_cpu)(void)
  18         __attribute__((visibility("hidden")));
  19
  20 #ifdef LTTNG_UST_DEBUG_VALGRIND
  21
  22 /*
  23  * Fallback on cpu 0 if liblttng-ust is build with Valgrind support.
  24  * get_cpu() returns the current CPU number. It may change due to
  25  * migration, so it is only statistically accurate.
  26  */
  27 static inline
  28 int lttng_ust_get_cpu_internal(void)
  29 {
  30         return 0;
  31 }
  32
  33 #else
  34
  35 /*
  36  * sched_getcpu.
  37  */
  38 #ifdef __linux__
  39
  40 #if !HAVE_SCHED_GETCPU
  41 #include <sys/syscall.h>
  42 #define __getcpu(cpu, node, cache)      syscall(__NR_getcpu, cpu, node, cache)
  43 /*
  44  * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
  45  */
  46 static inline
  47 int lttng_ust_get_cpu_internal(void)
  48 {
  49         int cpu, ret;
  50
  51         ret = __getcpu(&cpu, NULL, NULL);
  52         if (caa_unlikely(ret < 0))
  53                 return 0;
  54         return cpu;
  55 }
  56 #else /* HAVE_SCHED_GETCPU */
  57 #include <sched.h>
  58
  59 /*
  60  * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
  61  */
  62 static inline
  63 int lttng_ust_get_cpu_internal(void)
  64 {
  65         int cpu;
  66
  67         cpu = sched_getcpu();
  68         if (caa_unlikely(cpu < 0))
  69                 return 0;
  70         return cpu;
  71 }
  72 #endif  /* HAVE_SCHED_GETCPU */
  73
  74 #elif (defined(__FreeBSD__) || defined(__CYGWIN__))
  75
  76 /*
  77  * FreeBSD and Cygwin do not allow query of CPU ID. Always use CPU
  78  * number 0, with the assocated performance degradation on SMP.
  79  */
  80 static inline
  81 int lttng_ust_get_cpu_internal(void)
  82 {
  83         return 0;
  84 }
  85
  86 #else
  87 #error "Please add support for your OS into liblttng-ust/compat.h."
  88 #endif
  89
  90 #endif
  91
  92 static inline
  93 int lttng_ust_get_cpu(void)
  94 {
  95         int (*getcpu)(void) = CMM_LOAD_SHARED(lttng_get_cpu);
  96
  97         if (caa_likely(!getcpu)) {
  98                 return lttng_ust_get_cpu_internal();
  99         } else {
 100                 return getcpu();
 101         }
 102 }
 103
 104 #endif /* _LTTNG_GETCPU_H */