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authorRickard Green <[email protected]>2017-01-04 18:10:26 +0100
committerRickard Green <[email protected]>2017-01-17 12:23:19 +0100
commitf9459092940943876dff040ee997515b96fd5d50 (patch)
tree075fc1e01f6cc1cd1e398b9f52a0ee0f617065e4 /erts/doc/src
parentfd1fb9070333fe5b91f4528841a4b0fe71bbf096 (diff)
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Scheduler wall time support for dirty schedulers
Diffstat (limited to 'erts/doc/src')
-rw-r--r--erts/doc/src/erlang.xml97
1 files changed, 85 insertions, 12 deletions
diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index b3fab3874b..1f64d7be86 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -6415,12 +6415,17 @@ lists:map(
<c><anno>TotalTime</anno></c> is the total time duration since
<seealso marker="#system_flag_scheduler_wall_time">
<c>scheduler_wall_time</c></seealso>
- activation. The time unit is undefined and can be subject
- to change between releases, OSs, and system restarts.
- <c>scheduler_wall_time</c> is only to be used to
- calculate relative values for scheduler-utilization.
- <c><anno>ActiveTime</anno></c> can never exceed
- <c><anno>TotalTime</anno></c>.</p>
+ activation for the specific scheduler. Note that
+ activation time can differ significantly between
+ schedulers. Currently dirty schedulers are activated
+ at system start while normal schedulers are activated
+ some time after the <c>scheduler_wall_time</c>
+ functionality is enabled. The time unit is undefined
+ and can be subject to change between releases, OSs,
+ and system restarts. <c>scheduler_wall_time</c> is only
+ to be used to calculate relative values for scheduler
+ utilization. <c><anno>ActiveTime</anno></c> can never
+ exceed <c><anno>TotalTime</anno></c>.</p>
<p>The definition of a busy scheduler is when it is not idle
and is not scheduling (selecting) a process or port,
that is:</p>
@@ -6438,15 +6443,37 @@ lists:map(
<c>scheduler_wall_time</c></seealso> is turned off.</p>
<p>The list of scheduler information is unsorted and can
appear in different order between calls.</p>
+ <p>As of ERTS version 9.0, also dirty CPU schedulers will
+ be included in the result. That is, all scheduler threads
+ that are expected to handle CPU bound work. If you also
+ want information about dirty I/O schedulers, use
+ <seealso marker="#statistics_scheduler_wall_time_all"><c>statistics(scheduler_wall_time_all)</c></seealso>
+ instead.</p>
+
+ <p>Normal schedulers will have scheduler identifiers in
+ the range <c>1 =&lt; <anno>SchedulerId</anno> =&lt;
+ </c><seealso marker="#system_info_schedulers"><c>erlang:system_info(schedulers)</c></seealso>.
+ Dirty CPU schedulers will have scheduler identifiers in
+ the range <c>erlang:system_info(schedulers) &lt;
+ <anno>SchedulerId</anno> =&lt; erlang:system_info(schedulers)
+ +
+ </c><seealso marker="#system_info_dirty_cpu_schedulers"><c>erlang:system_info(dirty_cpu_schedulers)</c></seealso>.
+ </p>
+ <note><p>The different types of schedulers handle
+ specific types of jobs. Every job is assigned to a specific
+ scheduler type. Jobs can migrate between different schedulers
+ of the same type, but never between schedulers of different
+ types. This fact has to be taken under consideration when
+ evaluating the result returned.</p></note>
<p>Using <c>scheduler_wall_time</c> to calculate
- scheduler-utilization:</p>
+ 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 the user takes another snapshot and calculates
- scheduler-utilization per scheduler, for example:</p>
+ scheduler utilization per scheduler, for example:</p>
<pre>
> <input>Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</input>
ok
@@ -6461,11 +6488,32 @@ ok
{7,0.973237033077876},
{8,0.9741297293248656}]</pre>
<p>Using the same snapshots to calculate a total
- scheduler-utilization:</p>
+ 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>
+ {Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)),
+ TotalSchedulerUtilization = A/T.</input>
+0.9769136803764825</pre>
+ <p>Total scheduler utilization will equal <c>1.0</c> when
+ all schedulers have been active all the time between the
+ two measurements.</p>
+ <p>Another (probably more) useful value is to calculate
+ total scheduler utilization weighted against maximum amount
+ of available CPU time:</p>
+ <pre>
+> <input>WeightedSchedulerUtilization = (TotalSchedulerUtilization
+ * (erlang:system_info(schedulers)
+ + erlang:system_info(dirty_cpu_schedulers)))
+ / erlang:system_info(logical_processors_available).</input>
0.9769136803764825</pre>
+ <p>This weighted scheduler utilization will reach <c>1.0</c>
+ when schedulers are active the same amount of time as
+ maximum available CPU time. If more schedulers exist
+ than available logical processors, this value may
+ be greater than <c>1.0</c>.</p>
+ <p>As of ERTS version 9.0, the Erlang runtime system
+ with SMP support will as default have more schedulers
+ than logical processors. This due to the dirty schedulers.</p>
<note>
<p><c>scheduler_wall_time</c> is by default disabled. To
enable it, use
@@ -6476,6 +6524,31 @@ ok
<func>
<name name="statistics" arity="1" clause_i="12"/>
+ <fsummary>Information about each schedulers work time.</fsummary>
+ <desc>
+ <marker id="statistics_scheduler_wall_time_all"></marker>
+ <p>The same as
+ <seealso marker="#statistics_scheduler_wall_time"><c>statistics(scheduler_wall_time)</c></seealso>,
+ except that it also include information about all dirty I/O
+ schedulers.</p>
+ <p>Dirty IO schedulers will have scheduler identifiers in
+ the range
+ <seealso marker="#system_info_schedulers"><c>erlang:system_info(schedulers)</c></seealso><c>
+ +
+ </c><seealso marker="#system_info_dirty_cpu_schedulers"><c>erlang:system_info(dirty_cpu_schedulers)</c></seealso><c> &lt;
+ <anno>SchedulerId</anno> =&lt; erlang:system_info(schedulers)
+ + erlang:system_info(dirty_cpu_schedulers)
+ +
+ </c><seealso marker="#system_info_dirty_io_schedulers"><c>erlang:system_info(dirty_io_schedulers)</c></seealso>.</p>
+ <note><p>Note that work executing on dirty I/O schedulers
+ are expected to mainly wait for I/O. That is, when you
+ get high scheduler utilization on dirty I/O schedulers,
+ CPU utilization is <em>not</em> expected to be high due to
+ this work.</p></note>
+ </desc>
+ </func>
+ <func>
+ <name name="statistics" arity="1" clause_i="13"/>
<fsummary>Information about active processes and ports.</fsummary>
<desc><marker id="statistics_total_active_tasks"></marker>
<p>Returns the total amount of active processes and ports in
@@ -6495,7 +6568,7 @@ ok
</func>
<func>
- <name name="statistics" arity="1" clause_i="13"/>
+ <name name="statistics" arity="1" clause_i="14"/>
<fsummary>Information about the run-queue lengths.</fsummary>
<desc><marker id="statistics_total_run_queue_lengths"></marker>
<p>Returns the total length of the run queues. That is, the number
@@ -6515,7 +6588,7 @@ ok
</func>
<func>
- <name name="statistics" arity="1" clause_i="14"/>
+ <name name="statistics" arity="1" clause_i="15"/>
<fsummary>Information about wall clock.</fsummary>
<desc>
<p>Returns information about wall clock. <c>wall_clock</c> can