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 #include "ust-helper.h"
  15
  16 LTTNG_HIDDEN
  17 void lttng_ust_getcpu_init(void);
  18
  19 LTTNG_HIDDEN
  20 extern int (*lttng_get_cpu)(void);
  21
  22 #ifdef LTTNG_UST_DEBUG_VALGRIND
  23
  24 /*
  25  * Fallback on cpu 0 if liblttng-ust is build with Valgrind support.
  26  * get_cpu() returns the current CPU number. It may change due to
  27  * migration, so it is only statistically accurate.
  28  */
  29 static inline
  30 int lttng_ust_get_cpu_internal(void)
  31 {
  32         return 0;
  33 }
  34
  35 #else
  36
  37 /*
  38  * sched_getcpu.
  39  */
  40 #ifdef __linux__
  41
  42 #if !HAVE_SCHED_GETCPU
  43 #include <sys/syscall.h>
  44 #define __getcpu(cpu, node, cache)      syscall(__NR_getcpu, cpu, node, cache)
  45 /*
  46  * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
  47  */
  48 static inline
  49 int lttng_ust_get_cpu_internal(void)
  50 {
  51         int cpu, ret;
  52
  53         ret = __getcpu(&cpu, NULL, NULL);
  54         if (caa_unlikely(ret < 0))
  55                 return 0;
  56         return cpu;
  57 }
  58 #else /* HAVE_SCHED_GETCPU */
  59 #include <sched.h>
  60
  61 /*
  62  * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
  63  */
  64 static inline
  65 int lttng_ust_get_cpu_internal(void)
  66 {
  67         int cpu;
  68
  69         cpu = sched_getcpu();
  70         if (caa_unlikely(cpu < 0))
  71                 return 0;
  72         return cpu;
  73 }
  74 #endif  /* HAVE_SCHED_GETCPU */
  75
  76 #elif (defined(__FreeBSD__) || defined(__CYGWIN__))
  77
  78 /*
  79  * FreeBSD and Cygwin do not allow query of CPU ID. Always use CPU
  80  * number 0, with the assocated performance degradation on SMP.
  81  */
  82 static inline
  83 int lttng_ust_get_cpu_internal(void)
  84 {
  85         return 0;
  86 }
  87
  88 #else
  89 #error "Please add support for your OS into liblttng-ust/compat.h."
  90 #endif
  91
  92 #endif
  93
  94 static inline
  95 int lttng_ust_get_cpu(void)
  96 {
  97         int (*getcpu)(void) = CMM_LOAD_SHARED(lttng_get_cpu);
  98
  99         if (caa_likely(!getcpu)) {
 100                 return lttng_ust_get_cpu_internal();
 101         } else {
 102                 return getcpu();
 103         }
 104 }
 105
 106 #endif /* _LTTNG_GETCPU_H */