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
  26 void lttng_ust_getcpu_init(void);
  27
  28 extern int (*lttng_get_cpu)(void);
  29
  30 #ifdef LTTNG_UST_DEBUG_VALGRIND
  31
  32 /*
  33  * Fallback on cpu 0 if liblttng-ust is build with Valgrind support.
  34  * get_cpu() returns the current CPU number. It may change due to
  35  * migration, so it is only statistically accurate.
  36  */
  37 static inline
  38 int lttng_ust_get_cpu_internal(void)
  39 {
  40         return 0;
  41 }
  42
  43 #else
  44
  45 /*
  46  * sched_getcpu.
  47  */
  48 #ifdef __linux__
  49
  50 #if !HAVE_SCHED_GETCPU
  51 #include <sys/syscall.h>
  52 #define __getcpu(cpu, node, cache)      syscall(__NR_getcpu, cpu, node, cache)
  53 /*
  54  * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
  55  */
  56 static inline
  57 int lttng_ust_get_cpu_internal(void)
  58 {
  59         int cpu, ret;
  60
  61         ret = __getcpu(&cpu, NULL, NULL);
  62         if (caa_unlikely(ret < 0))
  63                 return 0;
  64         return cpu;
  65 }
  66 #else /* HAVE_SCHED_GETCPU */
  67 #include <sched.h>
  68
  69 /*
  70  * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
  71  */
  72 static inline
  73 int lttng_ust_get_cpu_internal(void)
  74 {
  75         int cpu;
  76
  77         cpu = sched_getcpu();
  78         if (caa_unlikely(cpu < 0))
  79                 return 0;
  80         return cpu;
  81 }
  82 #endif  /* HAVE_SCHED_GETCPU */
  83
  84 #elif (defined(__FreeBSD__) || defined(__CYGWIN__))
  85
  86 /*
  87  * FreeBSD and Cygwin do not allow query of CPU ID. Always use CPU
  88  * number 0, with the assocated performance degradation on SMP.
  89  */
  90 static inline
  91 int lttng_ust_get_cpu_internal(void)
  92 {
  93         return 0;
  94 }
  95
  96 #else
  97 #error "Please add support for your OS into liblttng-ust/compat.h."
  98 #endif
  99
 100 #endif
 101
 102 static inline
 103 int lttng_ust_get_cpu(void)
 104 {
 105         int (*getcpu)(void) = CMM_LOAD_SHARED(lttng_get_cpu);
 106
 107         if (caa_likely(!getcpu)) {
 108                 return lttng_ust_get_cpu_internal();
 109         } else {
 110                 return getcpu();
 111         }
 112 }
 113
 114 #endif /* _LTTNG_GETCPU_H */