dtrace.xml

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<chapter xml:id="features.dtrace" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <title>DTrace Dynamic Tracing</title>

 <sect1 xml:id="features.dtrace.introduction">
  <title>Introduction to PHP and DTrace</title>

  <para>
   DTrace is an always-available, low overhead, tracing framework
   available on a number of platforms including Solaris, macOS,
   Oracle Linux and BSD.  DTrace can trace operating system behavior
   and user program execution. It can display argument values and be
   used to infer performance statistics.  Probes are monitored by user
   created scripts written in the DTrace D scripting language. This
   allows efficient analysis of data points.
  </para>

  <para>
   PHP probes that are not being actively monitored by a user's DTrace
   D script do not contain instrumented code so there is no
   performance degradation during normal application execution.
   Probes that are being monitored incur an overhead low enough to
   generally allow DTrace monitoring on live production systems.
  </para>

  <para>
   PHP incorporates "User-level Statically Defined Tracing" (USDT)
   probes that are triggered at runtime. For example, when a D script
   is monitoring PHP's <literal>function-entry</literal> probe, then,
   every time a PHP script function is called, this probe is fired and
   the associated D script action code is executed.  This action code
   could, for example, print probe arguments such as the source file
   location of the PHP function. Or the action could aggregate data
   such as the number of times each function is called.
  </para>

  <para>
   Only the PHP USDT probes are described here.  Refer to external
   general and operating system-specific DTrace literature to see how
   DTrace can be used to trace arbitrary functions, and how it can be
   used to trace operating system behavior.  Note not all DTrace
   features are available in all DTrace implementations.
  </para>

  <para>
   The static DTrace probes in PHP can alternatively be used with the
   SystemTap facility on some Linux distributions.
  </para>
 </sect1>

 <sect1 xml:id="features.dtrace.dtrace">
  <title>Using PHP and DTrace</title>
  <para>
   PHP can be configured with DTrace static probes on platforms that
   support DTrace Dynamic Tracing.
  </para>

  <sect2 xml:id="features.dtrace.install">
   <title>Configuring PHP for DTrace Static Probes</title>

   <para>
    Refer to external platform specific documentation for enabling
    operating system DTrace support.  For example, on Oracle Linux
    boot a UEK3 kernel and do:

    <informalexample>
     <programlisting role="php">
<![CDATA[
# modprobe fasttrap
# chmod 666 /dev/dtrace/helper
]]>
     </programlisting>
    </informalexample>
   </para>
   <para>
    Instead of using <literal>chmod</literal>, you could instead use an
    ACL package rule to limit device access to a specific user.
   </para>

   <para>
    Build PHP with the <literal>--enable-dtrace</literal> configuration parameter:
    <informalexample>
     <programlisting role="php">
<![CDATA[
# ./configure --enable-dtrace ...
# make
# make install
]]>
     </programlisting>
    </informalexample>
   </para>
   <para>
    This enables the static probes in core PHP.  Any PHP extensions
    that provide their own probes should be built separately as shared
    extensions.
   </para>
  </sect2>

  <sect2 xml:id="features.dtrace.static-probes">
  <title>DTrace Static Probes in Core PHP</title>
  <table>
   <title>The following static probes are available in PHP</title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry>Probe Name</entry>
      <entry>Probe Description</entry>
      <entry>Probe Arguments</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry><literal>request-startup</literal></entry>
      <entry>Fires when a request starts.</entry>
      <entry>char *<varname>file</varname>, char *<varname>request_uri</varname>, char *<varname>request_method</varname></entry>
     </row>
     <row>
      <entry><literal>request-shutdown</literal></entry>
      <entry>Fires when a request shutdown.</entry>
      <entry>char *<varname>file</varname>, char *<varname>request_uri</varname>, char *<varname>request_method</varname></entry>
     </row>
     <row>
      <entry><literal>compile-file-entry</literal></entry>
      <entry>Fires when the compilation of a script starts.</entry>
      <entry>char *<varname>compile_file</varname>, char *<varname>compile_file_translated</varname></entry>
     </row>
     <row>
      <entry><literal>compile-file-return</literal></entry>
      <entry>Fires when the compilation of a script finishes.</entry>
      <entry>char *<varname>compile_file</varname>, char *<varname>compile_file_translated</varname></entry>
     </row>
     <row>
      <entry><literal>execute-entry</literal></entry>
      <entry>Fires when an opcode array is to be executed.  For
      example, it fires on function calls, includes, and generator
      resumes.</entry>
      <entry>char *<varname>request_file</varname>, int <varname>lineno</varname></entry>
     </row>
     <row>
      <entry><literal>execute-return</literal></entry>
      <entry>Fires after execution of an opcode array.</entry>
      <entry>char *<varname>request_file</varname>, int <varname>lineno</varname></entry>
     </row>
     <row>
      <entry><literal>function-entry</literal></entry>
      <entry>Fires when the PHP engine enters a PHP function or method call.</entry>
      <entry>char *<varname>function_name</varname>, char *<varname>request_file</varname>, int <varname>lineno</varname>, char *<varname>classname</varname>, char *<varname>scope</varname></entry>
     </row>
     <row>
      <entry><literal>function-return</literal></entry>
      <entry>Fires when the PHP engine returns from a PHP function or method call.</entry>
      <entry>char *<varname>function_name</varname>, char *<varname>request_file</varname>, int <varname>lineno</varname>, char *<varname>classname</varname>, char *<varname>scope</varname></entry>
     </row>
     <row>
      <entry><literal>exception-thrown</literal></entry>
      <entry>Fires when an exception is thrown.</entry>
      <entry>char *<varname>classname</varname></entry>
     </row>
     <row>
      <entry><literal>exception-caught</literal></entry>
      <entry>Fires when an exception is caught.</entry>
      <entry>char *<varname>classname</varname></entry>
     </row>
     <row>
      <entry><literal>error</literal></entry>
      <entry>Fires when an error occurs, regardless of the <link linkend="ini.error-reporting">error_reporting</link> level.</entry>
      <entry>char *<varname>errormsg</varname>, char *<varname>request_file</varname>, int <varname>lineno</varname></entry>
     </row>
    </tbody>
   </tgroup>
  </table>
  <para>
   PHP extensions may also have additional static probes.
  </para>
  </sect2>

  <sect2 xml:id="features.dtrace.list-probes">
   <title>Listing DTrace Static Probes in PHP</title>
   <para>
    To list available probes, start a PHP process and then run:
    <informalexample>
     <programlisting>
<![CDATA[
# dtrace -l
]]>
     </programlisting>
    </informalexample>
   </para>

   <para>
    The output will be similar to:
    <informalexample>
     <programlisting>
<![CDATA[
   ID   PROVIDER            MODULE                          FUNCTION NAME
   [ . . . ]
    4   php15271               php               dtrace_compile_file compile-file-entry
    5   php15271               php               dtrace_compile_file compile-file-return
    6   php15271               php                        zend_error error
    7   php15271               php  ZEND_CATCH_SPEC_CONST_CV_HANDLER exception-caught
    8   php15271               php     zend_throw_exception_internal exception-thrown
    9   php15271               php                 dtrace_execute_ex execute-entry
   10   php15271               php           dtrace_execute_internal execute-entry
   11   php15271               php                 dtrace_execute_ex execute-return
   12   php15271               php           dtrace_execute_internal execute-return
   13   php15271               php                 dtrace_execute_ex function-entry
   14   php15271               php                 dtrace_execute_ex function-return
   15   php15271               php              php_request_shutdown request-shutdown
   16   php15271               php               php_request_startup request-startup
]]>
     </programlisting>
    </informalexample>
   </para>

   <para>
    The Provider column values consist of <literal>php</literal> and
    the process id of the currently running PHP process.
   </para>

   <para>
    If the Apache web server is running, the module name might be, for
    example, <filename>libphp5.so</filename>, and there would be
    multiple blocks of listings, one per running Apache process.
   </para>

   <para>
    The Function column refers to PHP's internal C implementation
    function names where each provider is located.
   </para>

   <para>
    If a PHP process is not running, then no PHP probes will be shown.
   </para>
  </sect2>

  <sect2 xml:id="features.dtrace.examples">
   <title>DTrace with PHP Example</title>
   <para>
    This example shows the basics of the DTrace D scripting language.
    <example>
     <title><filename>all_probes.d</filename> for tracing all PHP Static Probes with DTrace</title>
     <programlisting>
<![CDATA[
#!/usr/sbin/dtrace -Zs

#pragma D option quiet

php*:::compile-file-entry
{
    printf("PHP compile-file-entry\n");
    printf("  compile_file              %s\n", copyinstr(arg0));
    printf("  compile_file_translated   %s\n", copyinstr(arg1));
}

php*:::compile-file-return
{
    printf("PHP compile-file-return\n");
    printf("  compile_file              %s\n", copyinstr(arg0));
    printf("  compile_file_translated   %s\n", copyinstr(arg1));
}

php*:::error
{
    printf("PHP error\n");
    printf("  errormsg                  %s\n", copyinstr(arg0));
    printf("  request_file              %s\n", copyinstr(arg1));
    printf("  lineno                    %d\n", (int)arg2);
}

php*:::exception-caught
{
    printf("PHP exception-caught\n");
    printf("  classname                 %s\n", copyinstr(arg0));
}

php*:::exception-thrown
{
    printf("PHP exception-thrown\n");
    printf("  classname                 %s\n", copyinstr(arg0));
}

php*:::execute-entry
{
    printf("PHP execute-entry\n");
    printf("  request_file              %s\n", copyinstr(arg0));
    printf("  lineno                    %d\n", (int)arg1);
}

php*:::execute-return
{
    printf("PHP execute-return\n");
    printf("  request_file              %s\n", copyinstr(arg0));
    printf("  lineno                    %d\n", (int)arg1);
}

php*:::function-entry
{
    printf("PHP function-entry\n");
    printf("  function_name             %s\n", copyinstr(arg0));
    printf("  request_file              %s\n", copyinstr(arg1));
    printf("  lineno                    %d\n", (int)arg2);
    printf("  classname                 %s\n", copyinstr(arg3));
    printf("  scope                     %s\n", copyinstr(arg4));
}

php*:::function-return
{
    printf("PHP function-return\n");
    printf("  function_name             %s\n", copyinstr(arg0));
    printf("  request_file              %s\n", copyinstr(arg1));
    printf("  lineno                    %d\n", (int)arg2);
    printf("  classname                 %s\n", copyinstr(arg3));
    printf("  scope                     %s\n", copyinstr(arg4));
}

php*:::request-shutdown
{
    printf("PHP request-shutdown\n");
    printf("  file                      %s\n", copyinstr(arg0));
    printf("  request_uri               %s\n", copyinstr(arg1));
    printf("  request_method            %s\n", copyinstr(arg2));
}

php*:::request-startup
{
    printf("PHP request-startup\n");
    printf("  file                      %s\n", copyinstr(arg0));
    printf("  request_uri               %s\n", copyinstr(arg1));
    printf("  request_method            %s\n", copyinstr(arg2));
}
]]>
     </programlisting>
    </example>
   </para>

   <para>
    This script uses the <literal>-Z</literal> option to
    <filename>dtrace</filename>, allowing it to be run when there is no
    PHP process executing.  If this option were omitted the script
    would immediately terminate because it knows none of the probes to
    be monitored are in existence.
   </para>

   <para>
    The script traces all core PHP static probe points throughout the
    duration of a running PHP script. Run the D script:
    <informalexample>
     <programlisting>
<![CDATA[
# ./all_probes.d
]]>
     </programlisting>
    </informalexample>
   </para>

   <para>
    Run a PHP script or application.  The monitoring D script will
    output each probe's arguments as it fires.
   </para>

   <para>
    When monitoring is complete, the D script can be terminated with a
    <keycombo action='simul'><keycap>CTRL</keycap><keycap>C</keycap></keycombo>.
   </para>

   <para>
    On multi-CPU machines the probe ordering might not appear to be
    sequential. This depends on which CPU was processing the probes,
    and how threads migrate across CPUs.  Displaying probe time stamps
    will help reduce confusion, for example:
    <informalexample>
     <programlisting>
<![CDATA[
php*:::function-entry
{
      printf("%lld: PHP function-entry ", walltimestamp);
      [ . . .]
}
]]>
     </programlisting>
    </informalexample>
   </para>
  </sect2>

  <sect2 xml:id="features.dtrace.references">
   &reftitle.seealso;
   <simplelist>
    <member><link linkend="oci8.dtrace">OCI8 and DTrace Dynamic Tracing</link></member>
   </simplelist>
  </sect2>
 </sect1>

 <sect1 xml:id="features.dtrace.systemtap">
  <title>Using SystemTap with PHP DTrace Static Probes</title>
  <para>
   On some Linux distributions, the SystemTap tracing utility can be
   used to trace PHP's static DTrace probes.  This is available with
   PHP 5.4.20 and PHP 5.5.
  </para>

  <sect2 xml:id="features.dtrace.systemtap-install">
   <title>Installing PHP with SystemTap</title>

   <para>
    Install the SystemTap SDT development package:
    <informalexample>
     <programlisting role="shell">
<![CDATA[
# yum install systemtap-sdt-devel
]]>
     </programlisting>
    </informalexample>
   </para>

   <para>
    Install PHP with the DTrace probes enabled:
    <informalexample>
     <programlisting role="shell">
<![CDATA[
# ./configure --enable-dtrace ...
# make
]]>
     </programlisting>
    </informalexample>
   </para>
  </sect2>

  <sect2 xml:id="features.dtrace.systemtap-list-probes">
   <title>Listing Static Probes with SystemTap</title>

   <para>
    The static probes in PHP can be listed using <filename>stap</filename>:
    <informalexample>
     <programlisting>
<![CDATA[
# stap -l 'process.provider("php").mark("*")' -c 'sapi/cli/php -i'
]]>
     </programlisting>
    </informalexample>
   </para>

   <para>
    This outputs:
    <informalexample>
     <programlisting>
<![CDATA[
process("sapi/cli/php").provider("php").mark("compile__file__entry")
process("sapi/cli/php").provider("php").mark("compile__file__return")
process("sapi/cli/php").provider("php").mark("error")
process("sapi/cli/php").provider("php").mark("exception__caught")
process("sapi/cli/php").provider("php").mark("exception__thrown")
process("sapi/cli/php").provider("php").mark("execute__entry")
process("sapi/cli/php").provider("php").mark("execute__return")
process("sapi/cli/php").provider("php").mark("function__entry")
process("sapi/cli/php").provider("php").mark("function__return")
process("sapi/cli/php").provider("php").mark("request__shutdown")
process("sapi/cli/php").provider("php").mark("request__startup")
]]>
     </programlisting>
    </informalexample>
   </para>
  </sect2>

  <sect2 xml:id="features.dtrace.systemtap-examples">
   <title>SystemTap with PHP Example</title>

   <para>
    <example>
     <title><filename>all_probes.stp</filename> for tracing all PHP Static Probes with SystemTap</title>
     <programlisting role="shell">
<![CDATA[
probe process("sapi/cli/php").provider("php").mark("compile__file__entry") {
    printf("Probe compile__file__entry\n");
    printf("  compile_file %s\n", user_string($arg1));
    printf("  compile_file_translated %s\n", user_string($arg2));
}
probe process("sapi/cli/php").provider("php").mark("compile__file__return") {
    printf("Probe compile__file__return\n");
    printf("  compile_file %s\n", user_string($arg1));
    printf("  compile_file_translated %s\n", user_string($arg2));
}
probe process("sapi/cli/php").provider("php").mark("error") {
    printf("Probe error\n");
    printf("  errormsg %s\n", user_string($arg1));
    printf("  request_file %s\n", user_string($arg2));
    printf("  lineno %d\n", $arg3);
}
probe process("sapi/cli/php").provider("php").mark("exception__caught") {
    printf("Probe exception__caught\n");
    printf("  classname %s\n", user_string($arg1));
}
probe process("sapi/cli/php").provider("php").mark("exception__thrown") {
    printf("Probe exception__thrown\n");
    printf("  classname %s\n", user_string($arg1));
}
probe process("sapi/cli/php").provider("php").mark("execute__entry") {
    printf("Probe execute__entry\n");
    printf("  request_file %s\n", user_string($arg1));
    printf("  lineno %d\n", $arg2);
}
probe process("sapi/cli/php").provider("php").mark("execute__return") {
    printf("Probe execute__return\n");
    printf("  request_file %s\n", user_string($arg1));
    printf("  lineno %d\n", $arg2);
}
probe process("sapi/cli/php").provider("php").mark("function__entry") {
    printf("Probe function__entry\n");
    printf("  function_name %s\n", user_string($arg1));
    printf("  request_file %s\n", user_string($arg2));
    printf("  lineno %d\n", $arg3);
    printf("  classname %s\n", user_string($arg4));
    printf("  scope %s\n", user_string($arg5));
}
probe process("sapi/cli/php").provider("php").mark("function__return") {
    printf("Probe function__return: %s\n", user_string($arg1));
    printf(" function_name %s\n", user_string($arg1));
    printf("  request_file %s\n", user_string($arg2));
    printf("  lineno %d\n", $arg3);
    printf("  classname %s\n", user_string($arg4));
    printf("  scope %s\n", user_string($arg5));
}
probe process("sapi/cli/php").provider("php").mark("request__shutdown") {
    printf("Probe request__shutdown\n");
    printf("  file %s\n", user_string($arg1));
    printf("  request_uri %s\n", user_string($arg2));
    printf("  request_method %s\n", user_string($arg3));
}
probe process("sapi/cli/php").provider("php").mark("request__startup") {
    printf("Probe request__startup\n");
    printf("  file %s\n", user_string($arg1));
    printf("  request_uri %s\n", user_string($arg2));
    printf("  request_method %s\n", user_string($arg3));
}
]]>
     </programlisting>
    </example>
   </para>
   <para>
    The above script will trace all core PHP static probe points
    throughout the duration of a running PHP script:
    <informalexample>
     <programlisting>
<![CDATA[
# stap -c 'sapi/cli/php test.php' all_probes.stp
]]>
     </programlisting>
    </informalexample>
   </para>
  </sect2>
 </sect1>
</chapter>

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