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