Merge branch 'sv-sched-percentage-option' into maint

* sv-sched-percentage-option:
  add erl option to set schedulers by percentages

OTP-11282

1 files changed, 39 insertions, 11 deletions

diff --git a/erts/doc/src/erl.xml b/erts/doc/src/erl.xml
index 70569b1c6c..c16b45856d 100644
--- a/erts/doc/src/erl.xml
+++ b/erts/doc/src/erl.xml
@@ -748,19 +748,47 @@
       </item>
       <tag><marker id="+S"><c><![CDATA[+S Schedulers:SchedulerOnline]]></c></marker></tag>
       <item>
-        <p>Sets the amount of scheduler threads to create and scheduler
-	  threads to set online when SMP support has been enabled.
-	  Valid range for both values are 1-1024. If the
-          Erlang runtime system is able to determine the amount
-          of logical processors configured and logical processors available,
-	  <c>Schedulers</c> will default to logical processors configured,
-	  and <c>SchedulersOnline</c> will default to logical processors
-	  available; otherwise, the default values will be 1. <c>Schedulers</c>
-	  may be omitted if <c>:SchedulerOnline</c> is not and vice versa. The
-	  amount of schedulers online can be changed at run time via
+        <p>Sets the number of scheduler threads to create and scheduler
+	  threads to set online when SMP support has been enabled. The maximum for
+	  both values is 1024. If the Erlang runtime system is able to determine the
+	  amount of logical processors configured and logical processors available,
+	  <c>Schedulers</c> will default to logical processors configured, and
+	  <c>SchedulersOnline</c> will default to logical processors available;
+	  otherwise, the default values will be 1. <c>Schedulers</c> may be omitted
+	  if <c>:SchedulerOnline</c> is not and vice versa. The number of schedulers
+	  online can be changed at run time via
 	  <seealso marker="erlang#system_flag_schedulers_online">erlang:system_flag(schedulers_online, SchedulersOnline)</seealso>.
 	</p>
-        <p>This flag will be ignored if the emulator doesn't have
+	<p>If <c>Schedulers</c> or <c>SchedulersOnline</c> is specified as a
+	  negative number, the value is subtracted from the default number of
+	  logical processors configured or logical processors available, respectively.
+	</p>
+	<p>Specifying the value 0 for <c>Schedulers</c> or <c>SchedulersOnline</c>
+	  resets the number of scheduler threads or scheduler threads online respectively
+	  to its default value.
+	</p>
+        <p>This option is ignored if the emulator doesn't have
+          SMP support enabled (see the <seealso marker="#smp">-smp</seealso>
+          flag).</p>
+      </item>
+      <tag><marker id="+SP"><c><![CDATA[+SP SchedulersPercentage:SchedulersOnlinePercentage]]></c></marker></tag>
+      <item>
+        <p>Similar to <seealso marker="#+S">+S</seealso> but uses percentages to set the
+	  number of scheduler threads to create, based on logical processors configured,
+	  and scheduler threads to set online, based on logical processors available, when
+	  SMP support has been enabled. Specified values must be greater than 0. For example,
+	  <c>+SP 50:25</c> sets the number of scheduler threads to 50% of the logical processors
+	  configured and the number of scheduler threads online to 25% of the logical processors available.
+	  <c>SchedulersPercentage</c> may be omitted if <c>:SchedulersOnlinePercentage</c> is
+	  not and vice versa. The number of schedulers online can be changed at run time via
+	  <seealso marker="erlang#system_flag_schedulers_online">erlang:system_flag(schedulers_online, SchedulersOnline)</seealso>.
+	</p>
+	<p>This option interacts with <seealso marker="#+S">+S</seealso> settings.
+	  For example, on a system with 8 logical cores configured and 8 logical cores
+	  available, the combination of the options <c>+S 4:4 +SP 50:25</c> (in either order)
+	  results in 2 scheduler threads (50% of 4) and 1 scheduler thread online (25% of 4).
+	</p>
+        <p>This option is ignored if the emulator doesn't have
           SMP support enabled (see the <seealso marker="#smp">-smp</seealso>
           flag).</p>
       </item>