src/lib/thread/numcpus.c

   1 /* Copyright (c) 2003-2004, Roger Dingledine
   2  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
   3  * Copyright (c) 2007-2021, The Tor Project, Inc. */
   4 /* See LICENSE for licensing information */
   5
   6 /**
   7  * \file numcpus.c
   8  * \brief Compute the number of CPUs configured on this system.
   9  **/
  10
  11 #include "orconfig.h"
  12 #include "lib/thread/numcpus.h"
  13 #include "lib/log/log.h"
  14 #include "lib/log/util_bug.h"
  15
  16 #ifdef HAVE_UNISTD_H
  17 #include <unistd.h>
  18 #endif
  19 #ifdef _WIN32
  20 #include <windows.h>
  21 #endif
  22
  23 #include <stdlib.h>
  24
  25 /** Implementation logic for compute_num_cpus(). */
  26 static int
  27 compute_num_cpus_impl(void)
  28 {
  29 #ifdef _WIN32
  30   SYSTEM_INFO info;
  31   memset(&info, 0, sizeof(info));
  32   GetSystemInfo(&info);
  33   if (info.dwNumberOfProcessors >= 1 && info.dwNumberOfProcessors < INT_MAX)
  34     return (int)info.dwNumberOfProcessors;
  35   else
  36     return -1;
  37 #elif defined(HAVE_SYSCONF)
  38 #ifdef _SC_NPROCESSORS_CONF
  39   long cpus_conf = sysconf(_SC_NPROCESSORS_CONF);
  40 #else
  41   long cpus_conf = -1;
  42 #endif
  43 #ifdef _SC_NPROCESSORS_ONLN
  44   long cpus_onln = sysconf(_SC_NPROCESSORS_ONLN);
  45 #else
  46   long cpus_onln = -1;
  47 #endif
  48   long cpus = -1;
  49
  50   if (cpus_conf > 0 && cpus_onln < 0) {
  51     cpus = cpus_conf;
  52   } else if (cpus_onln > 0 && cpus_conf < 0) {
  53     cpus = cpus_onln;
  54   } else if (cpus_onln > 0 && cpus_conf > 0) {
  55     if (cpus_onln < cpus_conf) {
  56       log_info(LD_GENERAL, "I think we have %ld CPUS, but only %ld of them "
  57                "are available. Telling Tor to only use %ld. You can over"
  58                "ride this with the NumCPUs option",
  59                cpus_conf, cpus_onln, cpus_onln);
  60     }
  61     cpus = cpus_onln;
  62   }
  63
  64   if (cpus >= 1 && cpus < INT_MAX)
  65     return (int)cpus;
  66   else
  67     return -1;
  68 #else
  69   return -1;
  70 #endif /* defined(_WIN32) || ... */
  71 }
  72
  73 /** This is an arbitrary number but at this point in time, it is not that
  74  * uncommon to see servers up to that amount of CPUs. Most servers will likely
  75  * be around 16 to 32 cores now. Lets take advantage of large machines! The
  76  * "NumCPUs" torrc option overrides this maximum. */
  77 #define MAX_DETECTABLE_CPUS 128
  78
  79 /** Return how many CPUs we are running with.  We assume that nobody is
  80  * using hot-swappable CPUs, so we don't recompute this after the first
  81  * time.  Return -1 if we don't know how to tell the number of CPUs on this
  82  * system.
  83  */
  84 int
  85 compute_num_cpus(void)
  86 {
  87   static int num_cpus = -2;
  88   if (num_cpus == -2) {
  89     num_cpus = compute_num_cpus_impl();
  90     tor_assert(num_cpus != -2);
  91     if (num_cpus > MAX_DETECTABLE_CPUS) {
  92       /* LCOV_EXCL_START */
  93       log_notice(LD_GENERAL, "Wow!  I detected that you have %d CPUs. I "
  94                  "will not autodetect any more than %d, though.  If you "
  95                  "want to configure more, set NumCPUs in your torrc",
  96                  num_cpus, MAX_DETECTABLE_CPUS);
  97       num_cpus = MAX_DETECTABLE_CPUS;
  98       /* LCOV_EXCL_STOP */
  99     }
 100   }
 101   return num_cpus;
 102 }