path: root/lib/runtime_tools/doc/src/msacc.xml

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  <header>
    <copyright>
      <year>2014</year><year>2014</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
    </legalnotice>

    <title>Microstate Accounting</title>
    <prepared>Lukas Larsson</prepared>
    <responsible></responsible>
    <docno>1</docno>
    <approved></approved>
    <checked></checked>
    <date>14-09-30</date>
    <rev>A</rev>
    <file>msacc.xml</file>
  </header>
  <module since="OTP 19.0">msacc</module>
  <modulesummary>Convenience functions for microstate accounting</modulesummary>
  <description>
    <p>This module implements some convenience functions for analyzing
    microstate accounting data. For details about how to use the basic api and
    what the different states represent see
    <seealso marker="erts:erlang#statistics_microstate_accounting"><c>
    erlang:statistics(microstate_accounting)</c></seealso>.</p>
    <marker id="msacc_print_example"></marker>
    <p><em>Basic Scenario</em></p>
    <pre>1> <input>msacc:start(1000).</input>
ok
2> <input>msacc:print().</input>
Average thread real-time    : 1000513 us
Accumulated system run-time :    2213 us
Average scheduler run-time  :    1076 us

        Thread      aux check_io emulator       gc    other     port    sleep

Stats per thread:
     async( 0)    0.00%    0.00%    0.00%    0.00%    0.00%    0.00%  100.00%
     async( 1)    0.00%    0.00%    0.00%    0.00%    0.00%    0.00%  100.00%
       aux( 1)    0.00%    0.00%    0.00%    0.00%    0.00%    0.00%   99.99%
 scheduler( 1)    0.00%    0.03%    0.13%    0.00%    0.01%    0.00%   99.82%
 scheduler( 2)    0.00%    0.00%    0.00%    0.00%    0.03%    0.00%   99.97%

Stats per type:
         async    0.00%    0.00%    0.00%    0.00%    0.00%    0.00%  100.00%
           aux    0.00%    0.00%    0.00%    0.00%    0.00%    0.00%   99.99%
     scheduler    0.00%    0.02%    0.06%    0.00%    0.02%    0.00%   99.89%
ok
</pre>
    <p>This first command enables microstate accounting for 1000 milliseconds.
    See <seealso marker="#start-0"><c>start/0</c></seealso>,
    <seealso marker="#stop-0"><c>stop/0</c></seealso>,
    <seealso marker="#reset-0"><c>reset/0</c></seealso> and
    <seealso marker="#start-1"><c>start/1</c></seealso> for more details.
    The second command prints the statistics gathered during that time.
    First three general statistics are printed.</p>
    <taglist>
      <tag>Average real-time</tag>
      <item>The average time spent collecting data in the threads.
      This should be close to the time which data was collected.
      </item>
      <tag>System run-time</tag>
      <item>The total run-time of all threads in the system.
      This is what you get if you call <c>msacc:stats(total_runtime,Stats).</c>
      </item>
      <tag>Average scheduler run-time</tag>
      <item>The average run-time for the schedulers.
      This is the average amount of time the schedulers did not sleep.</item>
    </taglist>
    <p>Then one column per state is printed with a the percentage of time this
    thread spent in the state out of it's own real-time. After the thread
    specific time, the accumulated time for each type of thread is printed in
    a similar format.</p>
    <p>Since we have the average real-time and the percentage spent in each
    state we can easily calculate the time spent in each state by multiplying
    <c>Average thread real-time</c> with <c>Thread state %</c>, i.e. to
    get the time Scheduler 1 spent in the emulator state we do
    <c>1000513us * 0.13% = 1300us</c>.</p>
  </description>
  <datatypes>
    <datatype>
      <name name="msacc_data"/>
    </datatype>
    <datatype>
      <name name="msacc_data_thread"/>
    </datatype>
    <datatype>
      <name name="msacc_data_counters"/>
      <desc><p>A map containing the different microstate accounting states and
      the number of microseconds spent in it.</p></desc>
    </datatype>
    <datatype>
      <name name="msacc_stats"/>
    </datatype>
    <datatype>
      <name name="msacc_stats_thread"/>
      <desc><p>A map containing information about a specific thread. The
      percentages in the map can be either run-time or real-time depending
      on if <c>runtime</c> or <c>realtime</c> was requested from
      <seealso marker="#stats-2">stats/2</seealso>. <c>system</c> is the
      percentage of total system time for this specific thread.</p></desc>
    </datatype>
    <datatype>
      <name name="msacc_stats_counters"/>
      <desc><p>A map containing the different microstate accounting states. Each
      value in the map contains another map with the percentage of time that
      this thread has spent in the specific state. Both the percentage of
      <c>system</c> time and the time for that specific <c>thread</c> is part of
      the map.</p></desc>
    </datatype>
    <datatype>
      <name name="msacc_type"/>
    </datatype>
    <datatype>
      <name name="msacc_id"/>
    </datatype>
    <datatype>
      <name name="msacc_state"/>
      <desc><p>The different states that a thread can be in. See
      <seealso marker="erts:erlang#statistics_microstate_accounting">
        erlang:statistics(microstate_accounting)</seealso> for details.
      </p></desc>
    </datatype>
    <datatype>
      <name name="msacc_print_options"/>
      <desc><p>The different options that can be given to
      <seealso marker="#print-2"><c>print/2</c></seealso>.
      </p></desc>
    </datatype>
  </datatypes>
  <funcs>
    <func>
      <name name="available" arity="0" since="OTP 19.0"/>
      <fsummary>Check if microstate accounting is available</fsummary>
      <desc>
	<p>This function checks whether microstate accounting
        is available or not.</p>
      </desc>
    </func>
    <func>
      <name name="start" arity="0" since="OTP 19.0"/>
      <fsummary>Start microstate accounting.</fsummary>
      <desc>
        <p>Start microstate accounting. Returns whether it was
        previously enabled or disabled.</p>
      </desc>
    </func>
    <func>
      <name name="start" arity="1" since="OTP 19.0"/>
      <fsummary>Start microstate accounting for a time.</fsummary>
      <desc>
        <p>Resets all counters and then starts microstate accounting
        for the given milliseconds.</p>
      </desc>
    </func>
    <func>
      <name name="stop" arity="0" since="OTP 19.0"/>
      <fsummary>Stop microstate accounting.</fsummary>
      <desc>
        <p>Stop microstate accounting.
        Returns whether is was previously enabled or disabled.</p>
      </desc>
    </func>
    <func>
      <name name="reset" arity="0" since="OTP 19.0"/>
      <fsummary>Reset microstate accounting counters</fsummary>
      <desc>
        <p>Reset microstate accounting counters.
        Returns whether is was enabled or disabled.</p>
      </desc>
    </func>
    <func>
      <name name="print" arity="0" since="OTP 19.0"/>
      <fsummary>Print microstate statistics</fsummary>
      <desc>
        <p>
          Prints the current microstate accounting to standard out.
          Same as
          <seealso marker="#print-1">
            <c>msacc:print(msacc:stats(),#{}).</c>
          </seealso>
        </p>
      </desc>
    </func>
    <func>
      <name name="print" arity="1" since="OTP 19.0"/>
      <fsummary>Print microstate statistics</fsummary>
      <desc>
        <p>Print the given microstate statistics values to stdout.
        Same as
        <seealso marker="#print-1">
          <c>msacc:print(DataOrStats,#{}).</c>
        </seealso>
        </p>
      </desc>
    </func>
    <func>
      <name name="print" arity="2" since="OTP 19.0"/>
      <fsummary>Print microstate statistics</fsummary>
      <desc>
        <p>Print the given microstate statistics values to standard out.
        With many states this can be quite verbose. See the top of this
        reference manual for a brief description of what the fields mean.</p>
        <p>It is possible to print more specific types of statistics by
        first manipulating the <c>DataOrStats</c> using
        <seealso marker="#stats-2"><c>stats/2</c></seealso>.
        For instance if you want to print the percentage of run-time for each
        thread you can do:</p>
        <pre><input>msacc:print(msacc:stats(runtime,msacc:stats())).</input></pre>
        <p>If you want to only print run-time per thread type you can do:</p>
        <pre><input>msacc:print(msacc:stats(type,msacc:stats(runtime,msacc:stats()))).</input></pre>
        <p><em>Options</em></p>
        <taglist>
          <tag><c>system</c></tag><item>Print percentage of time spent in each
          state out of system time as well as thread time.
          Default: false.</item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="print" arity="3" since="OTP 19.0"/>
      <fsummary>Print microstate statistics</fsummary>
      <desc>
        <p>Print the given microstate statistics values to the given file
        or device. The other arguments behave the same way as for
        <seealso marker="#print-2"><c>print/2</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="stats" arity="0" since="OTP 19.0"/>
      <fsummary></fsummary>
      <desc>
        <p>Returns a runtime system independent version of the microstate
        statistics data presented by
        <seealso marker="erts:erlang#statistics_microstate_accounting">
        <c>erlang:statistics(microstate_accounting)</c></seealso>.
        All counters have been normalized to be in microsecond resolution.</p>
      </desc>
    </func>
    <func>
      <name name="stats" arity="2" clause_i="1" since="OTP 19.0"/>
      <fsummary></fsummary>
      <desc>
        <p>Returns the system time for the given microstate statistics values.
        System time is the accumulated time of all threads.</p>
        <taglist>
          <tag><c>realtime</c></tag>
          <item>Returns all time recorded for all threads.</item>
          <tag><c>runtime</c></tag>
          <item>Returns all time spent doing work for all threads, i.e.
          all time not spent in the <c>sleep</c> state.</item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="stats" arity="2" clause_i="2" since="OTP 19.0"/>
      <fsummary></fsummary>
      <desc>
        <p>Returns fractions of real-time or run-time spent in the various
        threads from the given microstate statistics values.</p>
      </desc>
    </func>
    <func>
      <name name="stats" arity="2" clause_i="3" since="OTP 19.0"/>
      <fsummary></fsummary>
      <desc>
        <p>Returns a list of microstate statistics values where the values
        for all threads of the same type has been merged.</p>
      </desc>
    </func>
    <func>
      <name name="to_file" arity="1" since="OTP 19.0"/>
      <fsummary></fsummary>
      <desc>
        <p>Dumps the current microstate statistics counters to a file that can
        be parsed with <seealso marker="kernel:file#consult/1">
        file:consult/1</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="from_file" arity="1" since="OTP 19.0"/>
      <fsummary></fsummary>
      <desc>
        <p>Read a file dump produced by <seealso marker="#to_file/1">
        to_file(Filename)</seealso>.</p>
      </desc>
    </func>
  </funcs>
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