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-rw-r--r--erts/doc/src/erlang.xml116
1 files changed, 90 insertions, 26 deletions
diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index 4672c91a8f..30e3b02a0a 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -4352,11 +4352,12 @@ true</pre>
<name name="statistics" arity="1" clause_i="2"/>
<fsummary>Information about exact reductions</fsummary>
<desc>
- <p><marker id="statistics_exact_reductions"></marker>
- <em>NOTE:</em> <c>statistics(exact_reductions)</c> is
- a more expensive operation than
- <seealso marker="#statistics_reductions">statistics(reductions)</seealso>
- especially on an Erlang machine with SMP support.</p>
+ <marker id="statistics_exact_reductions"></marker>
+ <note><p><c>statistics(exact_reductions)</c> is
+ a more expensive operation than
+ <seealso marker="#statistics_reductions">statistics(reductions)</seealso>
+ especially on an Erlang machine with SMP support.</p>
+ </note>
</desc>
</func>
<func>
@@ -4364,6 +4365,10 @@ true</pre>
<fsummary>Information about garbage collection</fsummary>
<desc>
<p>This information may not be valid for all implementations.</p>
+ <pre>
+> <input>statistics(garbage_collection).</input>
+{85,23961,0}
+</pre>
</desc>
</func>
<func>
@@ -4379,12 +4384,18 @@ true</pre>
<name name="statistics" arity="1" clause_i="5"/>
<fsummary>Information about reductions</fsummary>
<desc>
- <p><marker id="statistics_reductions"></marker>
- <em>NOTE:</em> From erts version 5.5 (OTP release R11B)
- this value does not include reductions performed in current
- time slices of currently scheduled processes. If an
- exact value is wanted, use
- <seealso marker="#statistics_exact_reductions">statistics(exact_reductions)</seealso>.</p>
+ <marker id="statistics_reductions"></marker>
+ <note>
+ <p>Since erts-5.5 (OTP release R11B)
+ this value does not include reductions performed in current
+ time slices of currently scheduled processes. If an
+ exact value is wanted, use
+ <seealso marker="#statistics_exact_reductions">statistics(exact_reductions)</seealso>.</p>
+ </note>
+ <pre>
+> <input>statistics(reductions).</input>
+{2046,11}
+</pre>
</desc>
</func>
<func>
@@ -4402,25 +4413,78 @@ true</pre>
<p>Note that the run-time is the sum of the run-time for all
threads in the Erlang run-time system and may therefore be greater
than the wall-clock time.</p>
+ <pre>
+> <input>statistics(runtime).</input>
+{1690,1620}
+</pre>
</desc>
</func>
<func>
<name name="statistics" arity="1" clause_i="8"/>
<fsummary>Information about each schedulers work time</fsummary>
<desc>
- <p><marker id="statistics_scheduler_wall_time"></marker>
- Returns time lapsed (<c><anno>Scheduler_Total_Time</anno></c>) and time spent working
- (<c><anno>Scheduler_Worked_Time</anno></c>) for each scheduler since
- the system flag <seealso marker="#system_flag_scheduler_wall_time"><c>scheduler_wall_time</c></seealso>
- was set to <c>true</c>.</p>
- <p>
- Returns <c>undefined</c> if the system flag <seealso marker="#system_flag_scheduler_wall_time">
- <c>scheduler_wall_time</c></seealso> is set to <c>false</c>.
- </p>
- <p>The list of scheduler information is unsorted and may come in different order
- between calls. The time unit is undefined and may be changed and should only be used
- to calculate relative utilization.
- </p>
+ <marker id="statistics_scheduler_wall_time"></marker>
+ <p>
+ Returns a list of tuples with <c>{<anno>SchedulerId</anno>,
+ <anno>ActiveTime</anno>, <anno>TotalTime</anno>}</c>, where
+ <c>SchedulerId</c> is an integer id of the scheduler, <c>ActiveTime</c> is
+ the duration the scheduler has been busy, <c>TotalTime</c> is the total time duration since
+ <seealso marker="#system_flag_scheduler_wall_time">scheduler_wall_time</seealso>
+ activation. The time unit is not defined and may be subject to change
+ between releases, operating systems and system restarts.
+ <c>scheduler_wall_time</c> should only be used to calculate relative
+ values for scheduler-utilization. <c>ActiveTime</c> can never exceed <c>TotalTime</c>.
+ </p>
+
+ <p>The definition of a busy scheduler is when it is not idle or not
+ scheduling (selecting) a process or port, meaning; executing process
+ code, executing linked-in-driver or NIF code, executing
+ built-in-functions or any other runtime handling, garbage collecting
+ or handling any other memory management. Note, a scheduler may also be
+ busy even if the operating system has scheduled out the scheduler
+ thread.
+ </p>
+
+ <p>
+ Returns <c>undefined</c> if the system flag
+ <seealso marker="#system_flag_scheduler_wall_time">scheduler_wall_time</seealso>
+ is turned off.
+ </p>
+
+ <p>The list of scheduler information is unsorted and may appear in different order
+ between calls.
+ </p>
+ <p>Using <c>scheduler_wall_time</c> to calculate scheduler utilization.</p>
+<pre>
+> <input>erlang:system_flag(scheduler_wall_time, true).</input>
+false
+> <input>Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</input>
+ok
+</pre>
+ <p>Some time later we will take another snapshot and calculate scheduler-utilization per scheduler.</p>
+<pre>
+> <input>Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</input>
+ok
+> <input>lists:map(fun({{I, A0, T0}, {I, A1, T1}}) ->
+ {I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)).</input>
+[{1,0.9743474730177548},
+ {2,0.9744843782751444},
+ {3,0.9995902361669045},
+ {4,0.9738012596572161},
+ {5,0.9717956667018103},
+ {6,0.9739235846420741},
+ {7,0.973237033077876},
+ {8,0.9741297293248656}]
+</pre>
+ <p>Using the same snapshots to calculate a total scheduler-utilization.</p>
+<pre>
+> <input>{A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) ->
+ {Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), A/T.</input>
+0.9769136803764825
+</pre>
+ <note>
+ <p><c>scheduler_wall_time</c> is by default disabled. Use <c>erlang:system_flag(scheduler_wall_time, true)</c> to enable it. </p>
+ </note>
</desc>
</func>
<func>
@@ -4445,8 +4509,8 @@ true</pre>
<p>A process can be suspended by multiple processes and can
be suspended multiple times by a single process. A suspended
process will not leave the suspended state until its suspend
- count reach zero. The suspend count of <c><anno>Suspendee</anno></c> is
- decreased when
+ count reach zero. The suspend count of <c><anno>Suspendee</anno></c>
+ is decreased when
<seealso marker="#resume_process/1">erlang:resume_process(<anno>Suspendee</anno>)</seealso>
is called by the same process that called
<c>erlang:suspend_process(<anno>Suspendee</anno>)</c>. All increased suspend