libringbuffer/getcpu.h

   1 #ifndef _LTTNG_GETCPU_H
   2 #define _LTTNG_GETCPU_H
   3
   4 /*
   5  * Copyright (c) 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   6  *
   7  * This library is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; only
  10  * version 2.1 of the License.
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with this library; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 #include <urcu/compiler.h>
  23 #include <urcu/system.h>
  24 #include <urcu/arch.h>
  25 #include <config.h>
  26
  27 void lttng_ust_getcpu_init(void);
  28
  29 extern int (*lttng_get_cpu)(void);
  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 (*getcpu)(void) = CMM_LOAD_SHARED(lttng_get_cpu);
 107
 108         if (caa_likely(!getcpu)) {
 109                 return lttng_ust_get_cpu_internal();
 110         } else {
 111                 return getcpu();
 112         }
 113 }
 114
 115 #endif /* _LTTNG_GETCPU_H */