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authorLukas Larsson <[email protected]>2017-10-24 16:55:33 +0200
committerLukas Larsson <[email protected]>2017-10-31 10:42:56 +0100
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system: Add info to profiling effeciency guide
Diffstat (limited to 'system/doc/efficiency_guide/profiling.xml')
-rw-r--r--system/doc/efficiency_guide/profiling.xml157
1 files changed, 111 insertions, 46 deletions
diff --git a/system/doc/efficiency_guide/profiling.xml b/system/doc/efficiency_guide/profiling.xml
index f661abf285..f185456158 100644
--- a/system/doc/efficiency_guide/profiling.xml
+++ b/system/doc/efficiency_guide/profiling.xml
@@ -41,26 +41,33 @@
<p>Erlang/OTP contains several tools to help finding bottlenecks:</p>
<list type="bulleted">
- <item><c>fprof</c> provides the most detailed information about
- where the program time is spent, but it significantly slows down the
- program it profiles.</item>
-
- <item><p><c>eprof</c> provides time information of each function
- used in the program. No call graph is produced, but <c>eprof</c> has
- considerable less impact on the program it profiles.</p>
- <p>If the program is too large to be profiled by <c>fprof</c> or
- <c>eprof</c>, the <c>cover</c> and <c>cprof</c> tools can be used
- to locate code parts that are to be more thoroughly profiled using
- <c>fprof</c> or <c>eprof</c>.</p></item>
-
- <item><c>cover</c> provides execution counts per line per
- process, with less overhead than <c>fprof</c>. Execution counts
- can, with some caution, be used to locate potential performance
- bottlenecks.</item>
-
- <item><c>cprof</c> is the most lightweight tool, but it only
- provides execution counts on a function basis (for all processes,
- not per process).</item>
+ <item><p><seealso marker="tools:fprof"><c>fprof</c></seealso> provides
+ the most detailed information about where the program time is spent,
+ but it significantly slows down the program it profiles.</p></item>
+
+ <item><p><seealso marker="tools:eprof"><c>eprof</c></seealso> provides
+ time information of each function used in the program. No call graph is
+ produced, but <c>eprof</c> has considerable less impact on the program it
+ profiles.</p>
+ <p>If the program is too large to be profiled by <c>fprof</c> or
+ <c>eprof</c>, <c>cprof</c> can be used to locate code parts that
+ are to be more thoroughly profiled using <c>fprof</c> or <c>eprof</c>.</p></item>
+
+ <item><p><seealso marker="tools:cprof"><c>cprof</c></seealso> is the
+ most lightweight tool, but it only provides execution counts on a
+ function basis (for all processes, not per process).</p></item>
+
+ <item><p><seealso marker="runtime_tools:dbg"><c>dbg</c></seealso> is the
+ generic erlang tracing frontend. By using the <c>timestamp</c> or
+ <c>cpu_timestamp</c> options it can be used to time how long function
+ calls in a live system take.</p></item>
+
+ <item><p><seealso marker="tools:lcnt"><c>lcnt</c></seealso> is used
+ to find contention points in the Erlang Run-Time System's internal
+ locking mechanisms. It is useful when looking for bottlenecks in
+ interaction between process, port, ets tables and other entities
+ that can be run in parallel.</p></item>
+
</list>
<p>The tools are further described in
@@ -82,6 +89,42 @@
</section>
<section>
+ <title>Memory profiling</title>
+ <pre>eheap_alloc: Cannot allocate 1234567890 bytes of memory (of type "heap").</pre>
+ <p>The above slogan is one of the more common reasons for Erlang to terminate.
+ For unknown reasons the Erlang Run-Time System failed to allocate memory to
+ use. When this happens a crash dump is generated that contains information
+ about the state of the system as it ran out of mmeory. Use the
+ <seealso marker="observer:cdv"><c>crashdump_viewer</c></seealso> to get a
+ view of the memory is being used. Look for processes with large heaps or
+ many messages, large ets tables, etc.</p>
+ <p>When looking at memory usage in a running system the most basic function
+ to get information from is <seealso marker="erts:erlang#memory/0"><c>
+ erlang:memory()</c></seealso>. It returns the current memory usage
+ of the system. <seealso marker="tools:instrument"><c>instrument(3)</c></seealso>
+ can be used to get a more detailed breakdown of where memory is used.</p>
+ <p>Processes, ports and ets tables can then be inspecting using their
+ respective info functions, i.e.
+ <seealso marker="erts:erlang#process_info_memory"><c>erlang:process_info/2
+ </c></seealso>,
+ <seealso marker="erts:erlang#port_info_memory"><c>erlang:port_info/2
+ </c></seealso> and
+ <seealso marker="stdlib:ets#info/1"><c>ets:info/1</c></seealso>.
+ </p>
+ <p>Sometimes the system can enter a state where the reported memory
+ from <c>erlang:memory(total)</c> is very different from the
+ memory reported by the OS. This can be because of internal
+ fragmentation within the Erlang Run-Time System. Data about
+ how memory is allocated can be retrieved using
+ <seealso marker="erts:erlang#system_info_allocator">
+ <c>erlang:system_info(allocator)</c></seealso>.
+ The data you get from that function is very raw and not very plesant to read.
+ <url href="http://ferd.github.io/recon/recon_alloc.html">recon_alloc</url>
+ can be used to extract useful information from system_info
+ statistics counters.</p>
+ </section>
+
+ <section>
<title>Large Systems</title>
<p>For a large system, it can be interesting to run profiling
on a simulated and limited scenario to start with. But bottlenecks
@@ -94,6 +137,22 @@
tools on the whole system. Instead you want to concentrate on
central processes and modules, which contribute for a big part
of the execution.</p>
+
+ <p>There are also some tools that can be used to get a view of the
+ whole system with more or less overhead.</p>
+ <list type="bulleted">
+ <item><seealso marker="observer:observer"><c>observer</c></seealso>
+ is a GUI tool that can connect to remote nodes and display a
+ variety of information about the running system.</item>
+ <item><seealso marker="observer:etop"><c>etop</c></seealso>
+ is a command line tool that can connect to remote nodes and
+ display information similar to what the UNIX tool top shows.</item>
+ <item><seealso marker="runtime_tools:msacc"><c>msacc</c></seealso>
+ allows the user to get a view of what the Erlang Run-Time system
+ is spending its time doing. Has a very low overhead, which makes it
+ useful to run in heavily loaded systems to get some idea of where
+ to start doing more granular profiling.</item>
+ </list>
</section>
<section>
@@ -142,7 +201,7 @@
performance impact. Using <c>fprof</c> is just a matter of
calling a few library functions, see the
<seealso marker="tools:fprof">fprof</seealso> manual page in
- Tools .<c>fprof</c> was introduced in R8.</p>
+ Tools.</p>
</section>
<section>
@@ -156,20 +215,6 @@
</section>
<section>
- <title>cover</title>
- <p>The primary use of <c>cover</c> is coverage analysis to verify
- test cases, making sure that all relevant code is covered.
- <c>cover</c> counts how many times each executable line of code
- is executed when a program is run, on a per module basis.</p>
- <p>Clearly, this information can be used to determine what
- code is run very frequently and can therefore be subject for
- optimization. Using <c>cover</c> is just a matter of calling a
- few library functions, see the
- <seealso marker="tools:cover">cover</seealso> manual page in
- Tools.</p>
- </section>
-
- <section>
<title>cprof</title>
<p><c>cprof</c> is something in between <c>fprof</c> and
<c>cover</c> regarding features. It counts how many times each
@@ -216,16 +261,6 @@
<cell>No</cell>
</row>
<row>
- <cell><c>cover</c></cell>
- <cell>Per module to screen/file</cell>
- <cell>Small</cell>
- <cell>Moderate slowdown</cell>
- <cell>Yes, per line</cell>
- <cell>No</cell>
- <cell>No</cell>
- <cell>No</cell>
- </row>
- <row>
<cell><c>cprof</c></cell>
<cell>Per module to caller</cell>
<cell>Small</cell>
@@ -238,6 +273,37 @@
<tcaption>Tool Summary</tcaption>
</table>
</section>
+
+ <section>
+ <title>dbg</title>
+ <p><c>dbg</c> is a generic Erlang trace tool. By using the
+ <c>timestamp</c> or <c>cpu_timestamp</c> options it can be used
+ as a precision instrument to profile how long time a function
+ call takes for a specific process. This can be very useful when
+ trying to understand where time is spent in a heavily loaded
+ system as it is possible to limit the scope of what is profiled
+ to be very small.
+ For more information, see the
+ <seealso marker="runtime_tools:dbg">dbg</seealso> manual page in
+ Runtime Tools.</p>
+ </section>
+
+ <section>
+ <title>lcnt</title>
+ <p><c>lcnt</c> is used to profile interactions inbetween
+ entities that run in parallel. For example if you have
+ a process that all other processes in the system needs
+ to interact with (maybe it has some global configuration),
+ then <c>lcnt</c> can be used to figure out if the interaction
+ with that process is a problem.</p>
+ <p>In the Erlang Run-time System entities are only run in parallel
+ when there are multiple schedulers. Therefore <c>lcnt</c> will
+ show more contention points (and thus be more useful) on systems
+ using many schedulers on many cores.</p>
+ <p>For more information, see the
+ <seealso marker="tools:lcnt">lcnt</seealso> manual page in Tools.</p>
+ </section>
+
</section>
<section>
@@ -296,4 +362,3 @@
</list>
</section>
</chapter>
-