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 /* old uClibc versions didn't have sched_getcpu */
  51 #if defined(__UCLIBC__) && __UCLIBC_MAJOR__ == 0 && \
  52         (__UCLIBC_MINOR__ < 9 || \
  53          (__UCLIBC_MINOR__ == 9 && __UCLIBC_SUBLEVEL__ <= 32))
  54 #include <sys/syscall.h>
  55 #define __getcpu(cpu, node, cache)      syscall(__NR_getcpu, cpu, node, cache)
  56 /*
  57  * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
  58  */
  59 static inline
  60 int lttng_ust_get_cpu_internal(void)
  61 {
  62         int cpu, ret;
  63
  64         ret = __getcpu(&cpu, NULL, NULL);
  65         if (caa_unlikely(ret < 0))
  66                 return 0;
  67         return c;
  68 }
  69 #else /* __UCLIBC__ */
  70 #include <sched.h>
  71
  72 /*
  73  * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
  74  */
  75 static inline
  76 int lttng_ust_get_cpu_internal(void)
  77 {
  78         int cpu;
  79
  80         cpu = sched_getcpu();
  81         if (caa_unlikely(cpu < 0))
  82                 return 0;
  83         return cpu;
  84 }
  85 #endif  /* __UCLIBC__ */
  86
  87 #elif (defined(__FreeBSD__) || defined(__CYGWIN__))
  88
  89 /*
  90  * FreeBSD and Cygwin do not allow query of CPU ID. Always use CPU
  91  * number 0, with the assocated performance degradation on SMP.
  92  */
  93 static inline
  94 int lttng_ust_get_cpu_internal(void)
  95 {
  96         return 0;
  97 }
  98
  99 #else
 100 #error "Please add support for your OS into liblttng-ust/compat.h."
 101 #endif
 102
 103 #endif
 104
 105 static inline
 106 int lttng_ust_get_cpu(void)
 107 {
 108         int (*getcpu)(void) = CMM_LOAD_SHARED(lttng_get_cpu);
 109
 110         if (caa_likely(!getcpu)) {
 111                 return lttng_ust_get_cpu_internal();
 112         } else {
 113                 return getcpu();
 114         }
 115 }
 116
 117 #endif /* _LTTNG_GETCPU_H */