Changed default number of threads and added auto value.

Changed default number of threads to 1 instead of autoconfigured value and
added a new `auto` variable which enables autoconfiguration of thread count.

The number of threads used when autoconfiguratio fails was changed from 4 to 1.

The default value of using N threads where N is the number of CPU cores was
not optimal as the possibility of rescheduling was higher the more utility
threads there were. Due to this, N-1 is deemed to be the better autoconfigured
value for thread count.

Documentation/Getting-Started/Configuration-Guide.md

@@ -69,19 +69,20 @@ The global settings, in a section named `[MaxScale]`, allow various parameters t
 #### `threads`
 
 This parameter controls the number of worker threads that are handling the
-events coming from the kernel. MaxScale will auto-detect the number of
-processors of the system unless number of threads is manually configured.
-It is recommended that you let MaxScale detect how many cores the system
-has and leave this parameter undefined. The number of used cores will be
-logged into the message logs and if you are not satisfied with the
-auto-detected value, you can manually configure it. Increasing the amount
-of worker threads beyond the number of processor cores does not improve
-the performance, rather is likely to degrade it, and can consume resources
-needlessly.
+events coming from the kernel. The default is 1 thread. It is recommended that
+you start with one thread and increase the number if you require greater
+performance. Increasing the amount of worker threads beyond the number of
+processor cores does not improve the performance, rather is likely to degrade
+it, and can consume resources needlessly.
+
+You can enable automatic configuration of this value by setting the value to
+`auto`. This way MaxScale will detect the number of available processors and
+set the amount of threads to be equal to that number. This should only be used
+for systems dedicated for running MaxScale.
 
 ```
 # Valid options are:
-#       threads=<number of epoll threads>
+#       threads=[<number of threads> | auto ]
 
 [MaxScale]
 threads=1

server/core/config.c

@@ -1577,11 +1577,28 @@ handle_global_item(const char *name, const char *value)
 {
     int i;
     if (strcmp(name, "threads") == 0)
+    {
+        if (strcmp(name, "auto") == 0)
+        {
+            if ((gateway.n_threads = get_processor_count()) > 1)
+            {
+                gateway.n_threads--;
+            }
+        }
+        else
         {
             int thrcount = atoi(value);
             if (thrcount > 0)
             {
                 gateway.n_threads = thrcount;
+
+                int processor_count = get_processor_count();
+                if (thrcount > processor_count)
+                {
+                    MXS_WARNING("Number of threads set to %d which is greater than"
+                                " the number of processors available: %d",
+                                thrcount, processor_count);
+                }
             }
             else
             {
@@ -1589,6 +1606,7 @@ handle_global_item(const char *name, const char *value)
                 return 0;
             }
         }
+    }
     else if (strcmp(name, "non_blocking_polls") == 0)
     {
         gateway.n_nbpoll = atoi(value);
@@ -1706,7 +1724,7 @@ global_defaults()
 {
     uint8_t mac_addr[6]="";
     struct utsname uname_data;
-    gateway.n_threads = get_processor_count();
+    gateway.n_threads = DEFAULT_NTHREADS;
     gateway.n_nbpoll = DEFAULT_NBPOLLS;
     gateway.pollsleep = DEFAULT_POLLSLEEP;
     gateway.auth_conn_timeout = DEFAULT_AUTH_CONNECT_TIMEOUT;

server/core/gw_utils.c

@@ -237,8 +237,8 @@ long get_processor_count()
 #ifdef _SC_NPROCESSORS_ONLN
     if ((processors = sysconf(_SC_NPROCESSORS_ONLN)) <= 0)
     {
-        MXS_WARNING("Unable to establish the number of available cores. Defaulting to 4.");
-        processors = 4;
+        MXS_WARNING("Unable to establish the number of available cores. Defaulting to 1.");
+        processors = 1;
     }
 #else
 #error _SC_NPROCESSORS_ONLN not available.

server/include/maxconfig.h

@@ -41,6 +41,7 @@
 #define		DEFAULT_POLLSLEEP	1000	/**< Default poll wait time (milliseconds) */
 #define		_SYSNAME_STR_LENGTH	256	/**< sysname len */
 #define		_RELEASE_STR_LENGTH	256	/**< release len */
+#define		DEFAULT_NTHREADS	1 /**< Default number of polling threads */
 /**
  * Maximum length for configuration parameter value.
  */

server/maxscale_template.cnf

@@ -3,12 +3,11 @@
 
 # Global parameters
 #
-# Number of threads is autodetected, uncomment for manual configuration
 # Complete list of configuration options:
 # https://github.com/mariadb-corporation/MaxScale/blob/master/Documentation/Getting-Started/Configuration-Guide.md
 
 [maxscale]
-#threads=8
+threads=1
 
 # Server definitions
 #