my_getncpus based on threads available

Detecting the cpus based on sysconf of the online CPUs can significantly
over estimate the number of cpus available.

Wheither via numactl, cgroups, taskset, systemd constraints, docker
containers and probably other mechanisms, the number of threads mysqld
can be run on can be quite less.

As such we use the pthread_getaffinity_np function on Linux and FreeBSD
(identical API) to get the number of CPUs.

The number of CPUs is the default for the thread_pool_size and a too
high default will resulting in large memory usage and high context
switching overhead.

Closes PR #922

cmake/os/WindowsCache.cmake

@@ -127,6 +127,8 @@ SET(HAVE_PTHREAD_ATTR_GETSTACKSIZE CACHE  INTERNAL "")
 SET(HAVE_PTHREAD_ATTR_SETSCOPE CACHE  INTERNAL "")
 SET(HAVE_PTHREAD_ATTR_SETSTACKSIZE CACHE  INTERNAL "")
 SET(HAVE_PTHREAD_CONDATTR_CREATE CACHE  INTERNAL "")
+SET(HAVE_PTHREAD_CONDATTR_SETCLOCK CACHE  INTERNAL "")
+SET(HAVE_PTHREAD_GETAFFINITY_NP CACHE  INTERNAL "")
 SET(HAVE_PTHREAD_INIT CACHE  INTERNAL "")
 SET(HAVE_PTHREAD_KEY_DELETE CACHE  INTERNAL "")
 SET(HAVE_PTHREAD_RWLOCK_RDLOCK CACHE  INTERNAL "")

config.h.cmake

@@ -200,6 +200,9 @@
 #cmakedefine HAVE_PTHREAD_ATTR_SETSCOPE 1
 #cmakedefine HAVE_PTHREAD_ATTR_SETSTACKSIZE 1
 #cmakedefine HAVE_PTHREAD_CONDATTR_CREATE 1
+#cmakedefine HAVE_PTHREAD_CONDATTR_SETCLOCK 1
+#cmakedefine HAVE_PTHREAD_GETAFFINITY_NP 1
+#cmakedefine HAVE_PTHREAD_KEY_DELETE 1
 #cmakedefine HAVE_PTHREAD_KEY_DELETE 1
 #cmakedefine HAVE_PTHREAD_KILL 1
 #cmakedefine HAVE_PTHREAD_RWLOCK_RDLOCK 1

configure.cmake

@@ -375,6 +375,8 @@ CHECK_FUNCTION_EXISTS (pthread_attr_setscope HAVE_PTHREAD_ATTR_SETSCOPE)
 CHECK_FUNCTION_EXISTS (pthread_attr_getguardsize HAVE_PTHREAD_ATTR_GETGUARDSIZE)
 CHECK_FUNCTION_EXISTS (pthread_attr_setstacksize HAVE_PTHREAD_ATTR_SETSTACKSIZE)
 CHECK_FUNCTION_EXISTS (pthread_condattr_create HAVE_PTHREAD_CONDATTR_CREATE)
+CHECK_FUNCTION_EXISTS (pthread_condattr_setclock HAVE_PTHREAD_CONDATTR_SETCLOCK)
+CHECK_FUNCTION_EXISTS (pthread_getaffinity_np HAVE_PTHREAD_GETAFFINITY_NP)
 CHECK_FUNCTION_EXISTS (pthread_key_delete HAVE_PTHREAD_KEY_DELETE)
 CHECK_FUNCTION_EXISTS (pthread_rwlock_rdlock HAVE_PTHREAD_RWLOCK_RDLOCK)
 CHECK_FUNCTION_EXISTS (pthread_sigmask HAVE_PTHREAD_SIGMASK)

mysys/my_getncpus.c

@@ -21,10 +21,36 @@
 #include <unistd.h>
 #endif
 
+#if defined(__FreeBSD__) && defined(HAVE_PTHREAD_GETAFFINITY_NP)
+#include <pthread_np.h>
+#include <sys/cpuset.h>
+#endif
+
 static int ncpus=0;
 
-int my_getncpus()
+int my_getncpus(void)
 {
+#if (defined(__linux__) || defined(__FreeBSD__)) && defined(HAVE_PTHREAD_GETAFFINITY_NP)
+  cpu_set_t set;
+
+  if (!ncpus)
+  {
+    if (pthread_getaffinity_np(pthread_self(), sizeof(set), &set) == 0)
+    {
+      ncpus= CPU_COUNT(&set);
+    }
+    else
+    {
+#ifdef _SC_NPROCESSORS_ONLN
+      ncpus= sysconf(_SC_NPROCESSORS_ONLN);
+#else
+      ncpus= 2;
+#endif
+    }
+  }
+
+#else /* __linux__ || FreeBSD && HAVE_PTHREAD_GETAFFINITY_NP */
+
   if (!ncpus)
   {
 #ifdef _SC_NPROCESSORS_ONLN
@@ -46,5 +72,8 @@ int my_getncpus()
     ncpus= 2;
 #endif
   }
+
+#endif /* __linux__ || FreeBSD && HAVE_PTHREAD_GETAFFINITY_NP */
+
   return ncpus;
 }