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-rw-r--r--erts/doc/src/erlang.xml177
1 files changed, 164 insertions, 13 deletions
diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index 6915b35fcb..ddca492040 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -5870,6 +5870,146 @@ true</pre>
<func>
<name name="statistics" arity="1" clause_i="6"/>
+ <fsummary>Information about microstate accounting.</fsummary>
+ <desc>
+ <marker id="statistics_microstate_accounting"></marker>
+ <p>
+ Microstate accounting can be used to measure how much time the Erlang
+ runtime system spends doing various tasks. It is designed to be as
+ lightweight as possible, but there will be some overhead when this
+ is enabled. Microstate accounting is meant to be a profiling tool
+ to help figure out performance bottlenecks.
+ To <c>start</c>/<c>stop</c>/<c>reset</c> microstate_accounting you use
+ the system_flag
+ <seealso marker="#system_flag_microstate_accounting">
+ <c>microstate_accounting</c></seealso>.
+ </p>
+ <p>
+ <c>erlang:statistics(microstate_accounting)</c> returns a list of maps
+ representing some of the OS threads within ERTS. Each map contains
+ <c>type</c> and <c>id</c> fields that can be used to identify what
+ thread it is, and also a counters field that contains data about how
+ much time has been spent in the various states.</p>
+ <pre>
+> <input>erlang:statistics(microstate_accounting).</input>
+[#{counters => #{aux => 1899182914,
+ check_io => 2605863602,
+ emulator => 45731880463,
+ gc => 1512206910,
+ other => 5421338456,
+ port => 221631,
+ sleep => 5150294100},
+ id => 1,
+ type => scheduler}|...]
+ </pre>
+ <p>The time unit is the same as returned by
+ <seealso marker="kernel:os#perf_counter/0">
+ <c>os:perf_counter/0</c></seealso>.
+ So to convert it to milliseconds you could do something like this:</p>
+ <pre>
+lists:map(
+ fun(#{ counters := Cnt } = M) ->
+ MsCnt = maps:map(fun(_K, PerfCount) ->
+ erlang:convert_time_unit(PerfCount, perf_counter, 1000)
+ end, Cnt),
+ M#{ counters := MsCnt }
+ end, erlang:statistics(microstate_accounting)).
+ </pre>
+ <p>
+ It is important to note that these values are not guaranteed to be
+ the exact time spent in each state. This is because of various
+ optimisation done in order to keep the overhead as small as possible.
+ </p>
+
+ <p>Currently the following <c><anno>MSAcc_Thread_Type</anno></c> are available:</p>
+ <taglist>
+ <tag><c>scheduler</c></tag>
+ <item>The main execution threads that do most of the work.</item>
+ <tag><c>async</c></tag><item>Async threads are used by various
+ linked-in drivers (mainly the file drivers) do offload non-cpu
+ intensive work.</item>
+ <tag><c>aux</c></tag><item>Takes care of any work that is not
+ specifically assigned to a scheduler.</item>
+ </taglist>
+ <p>Currently the following <c><anno>MSAcc_Thread_State</anno></c>s are available.
+ All states are exclusive, meaning that a thread cannot be in two states
+ at once. So if you add the numbers of all counters in a thread
+ you will get the total run-time for that thread.</p>
+ <taglist>
+ <tag><c>aux</c></tag>
+ <item>Time spent handling auxiliary jobs.</item>
+ <tag><c>check_io</c></tag>
+ <item>Time spent checking for new I/O events.</item>
+ <tag><c>emulator</c></tag>
+ <item>Time spent executing erlang processes.</item>
+ <tag><c>gc</c></tag>
+ <item>Time spent doing garbage collection. When extra states are
+ enabled this is the time spent doing non-fullsweep garbage
+ collections.</item>
+ <tag><c>other</c></tag>
+ <item>Time spent doing unaccounted things.</item>
+ <tag><c>port</c></tag>
+ <item>Time spent executing ports.</item>
+ <tag><c>sleep</c></tag>
+ <item>Time spent sleeping.</item>
+ </taglist>
+ <p>It is possible to add more fine grained <c><anno>MSAcc_Thread_State</anno></c>s
+ through configure.
+ (e.g. <c>./configure --with-microstate-accounting=extra</c>).
+ Enabling these states will cause a performance degradation when
+ microstate accounting is turned off and increase the overhead when
+ it is turned on.</p>
+ <taglist>
+ <tag><c>alloc</c></tag>
+ <item>Time spent managing memory. Without extra states this time is
+ spread out over all other states.</item>
+ <tag><c>bif</c></tag>
+ <item>Time spent in bifs. Without extra states this time is part of
+ the <c>emulator</c> state.</item>
+ <tag><c>busy_wait</c></tag>
+ <item>Time spent busy waiting. This is also the state where a
+ scheduler no longer reports that it is active when using
+ <seealso marker="#statistics_scheduler_wall_time">
+ <c>erlang:statistics(scheduler_wall_time)</c></seealso>.
+ So if you add all other states but this and sleep and then divide that
+ by all time in the thread you should get something very similar to the
+ scheduler_wall_time fraction. Without extra states this time is part
+ of the <c>other</c> state.</item>
+ <tag><c>ets</c></tag>
+ <item>Time spent executing ETS bifs. Without extra states this time is
+ part of the <c>emulator</c> state.</item>
+ <tag><c>gc_full</c></tag>
+ <item>Time spent doing fullsweep garbage collection. Without extra
+ states this time is part of the <c>gc</c> state.</item>
+ <tag><c>nif</c></tag>
+ <item>Time spent in nifs. Without extra states this time is part of
+ the <c>emulator</c> state.</item>
+ <tag><c>send</c></tag>
+ <item>Time spent sending messages (processes only). Without extra
+ states this time is part of the <c>emulator</c> state.</item>
+ <tag><c>timers</c></tag>
+ <item>Time spent managing timers. Without extra states this time is
+ part of the <c>other</c> state.</item>
+ </taglist>
+ <p>There is a utility module called
+ <seealso marker="runtime_tools:msacc"><c>msacc</c></seealso> in
+ runtime_tools that can be used to more easily analyse these
+ statistics.</p>
+
+ <p>
+ Returns <c>undefined</c> if the system flag
+ <seealso marker="#system_flag_microstate_accounting">
+ <c>microstate_accounting</c></seealso>
+ is turned off.
+ </p>
+ <p>The list of thread information is unsorted and may appear in
+ different order between calls.</p>
+ <note><p>The threads and states are subject to change without any
+ prior notice.</p></note>
+ </desc>
+ </func>
+ <func>
+ <name name="statistics" arity="1" clause_i="7"/>
<fsummary>Information about reductions.</fsummary>
<desc>
<marker id="statistics_reductions"></marker>
@@ -5887,7 +6027,7 @@ true</pre>
</func>
<func>
- <name name="statistics" arity="1" clause_i="7"/>
+ <name name="statistics" arity="1" clause_i="8"/>
<fsummary>Information about the run-queues.</fsummary>
<desc><marker id="statistics_run_queue"></marker>
<p>
@@ -5903,7 +6043,7 @@ true</pre>
</func>
<func>
- <name name="statistics" arity="1" clause_i="8"/>
+ <name name="statistics" arity="1" clause_i="9"/>
<fsummary>Information about the run-queue lengths.</fsummary>
<desc><marker id="statistics_run_queue_lengths"></marker>
<p>
@@ -5923,7 +6063,7 @@ true</pre>
</func>
<func>
- <name name="statistics" arity="1" clause_i="9"/>
+ <name name="statistics" arity="1" clause_i="10"/>
<fsummary>Information about runtime.</fsummary>
<desc>
<p>Returns information about runtime, in milliseconds.</p>
@@ -5938,7 +6078,7 @@ true</pre>
</func>
<func>
- <name name="statistics" arity="1" clause_i="10"/>
+ <name name="statistics" arity="1" clause_i="11"/>
<fsummary>Information about each schedulers work time.</fsummary>
<desc>
<marker id="statistics_scheduler_wall_time"></marker>
@@ -6009,7 +6149,7 @@ ok
</func>
<func>
- <name name="statistics" arity="1" clause_i="11"/>
+ <name name="statistics" arity="1" clause_i="12"/>
<fsummary>Information about active processes and ports.</fsummary>
<desc><marker id="statistics_total_active_tasks"></marker>
<p>
@@ -6027,7 +6167,7 @@ ok
</func>
<func>
- <name name="statistics" arity="1" clause_i="12"/>
+ <name name="statistics" arity="1" clause_i="13"/>
<fsummary>Information about the run-queue lengths.</fsummary>
<desc><marker id="statistics_total_run_queue_lengths"></marker>
<p>
@@ -6046,7 +6186,7 @@ ok
</func>
<func>
- <name name="statistics" arity="1" clause_i="13"/>
+ <name name="statistics" arity="1" clause_i="14"/>
<fsummary>Information about wall clock.</fsummary>
<desc>
<p>Returns information about wall clock. <c>wall_clock</c> can
@@ -6280,6 +6420,17 @@ ok
<func>
<name name="system_flag" arity="2" clause_i="5"/>
+ <fsummary>Set system flag microstate_accounting</fsummary>
+ <desc><p><marker id="system_flag_microstate_accounting"></marker>
+ Turns on/off microstate accounting measurements. By passing reset it is possible to reset
+ all counters to 0.</p>
+ <p>For more information see,
+ <seealso marker="#statistics_microstate_accounting">erlang:statistics(microstate_accounting)</seealso>.
+ </p>
+ </desc>
+ </func>
+ <func>
+ <name name="system_flag" arity="2" clause_i="6"/>
<fsummary>Sets system flag <c>min_heap_size</c>.</fsummary>
<desc>
<p>Sets the default minimum heap size for processes. The size
@@ -6294,7 +6445,7 @@ ok
</func>
<func>
- <name name="system_flag" arity="2" clause_i="6"/>
+ <name name="system_flag" arity="2" clause_i="7"/>
<fsummary>Sets system flag <c>min_bin_vheap_size</c>.</fsummary>
<desc>
<p>Sets the default minimum binary virtual heap size for
@@ -6311,7 +6462,7 @@ ok
</func>
<func>
- <name name="system_flag" arity="2" clause_i="7"/>
+ <name name="system_flag" arity="2" clause_i="8"/>
<fsummary>Sets system flag <c>multi_scheduling</c>.</fsummary>
<desc>
<p><marker id="system_flag_multi_scheduling"></marker>
@@ -6349,7 +6500,7 @@ ok
</func>
<func>
- <name name="system_flag" arity="2" clause_i="8"/>
+ <name name="system_flag" arity="2" clause_i="9"/>
<fsummary>Sets system flag <c>scheduler_bind_type</c>.</fsummary>
<type name="scheduler_bind_type"/>
<desc>
@@ -6467,7 +6618,7 @@ ok
</func>
<func>
- <name name="system_flag" arity="2" clause_i="9"/>
+ <name name="system_flag" arity="2" clause_i="10"/>
<fsummary>Sets system flag <c>scheduler_wall_time</c>.</fsummary>
<desc><p><marker id="system_flag_scheduler_wall_time"></marker>
Turns on or off scheduler wall time measurements.</p>
@@ -6477,7 +6628,7 @@ ok
</func>
<func>
- <name name="system_flag" arity="2" clause_i="10"/>
+ <name name="system_flag" arity="2" clause_i="11"/>
<fsummary>Sets system flag <c>schedulers_online</c>.</fsummary>
<desc>
<p><marker id="system_flag_schedulers_online"></marker>
@@ -6502,7 +6653,7 @@ ok
</func>
<func>
- <name name="system_flag" arity="2" clause_i="11"/>
+ <name name="system_flag" arity="2" clause_i="12"/>
<fsummary>Sets system flag <c>trace_control_word</c>.</fsummary>
<desc>
<p>Sets the value of the node trace control word to