+ <h3>Choosing an MPM</h3>
+
+
+
+ <p>Apache 2.x supports pluggable concurrency models, called
+ <a href="../mpm.html">Multi-Processing Modules</a> (MPMs).
+ When building Apache, you must choose an MPM to use. There
+ are platform-specific MPMs for some platforms:
+ <code class="module"><a href="../mod/beos.html">beos</a></code>, <code class="module"><a href="../mod/mpm_netware.html">mpm_netware</a></code>,
+ <code class="module"><a href="../mod/mpmt_os2.html">mpmt_os2</a></code>, and <code class="module"><a href="../mod/mpm_winnt.html">mpm_winnt</a></code>. For
+ general Unix-type systems, there are several MPMs from which
+ to choose. The choice of MPM can affect the speed and scalability
+ of the httpd:</p>
+
+ <ul>
+
+ <li>The <code class="module"><a href="../mod/worker.html">worker</a></code> MPM uses multiple child
+ processes with many threads each. Each thread handles
+ one connection at a time. Worker generally is a good
+ choice for high-traffic servers because it has a smaller
+ memory footprint than the prefork MPM.</li>
+
+ <li>The <code class="module"><a href="../mod/prefork.html">prefork</a></code> MPM uses multiple child
+ processes with one thread each. Each process handles
+ one connection at a time. On many systems, prefork is
+ comparable in speed to worker, but it uses more memory.
+ Prefork's threadless design has advantages over worker
+ in some situations: it can be used with non-thread-safe
+ third-party modules, and it is easier to debug on platforms
+ with poor thread debugging support.</li>
+
+ </ul>
+
+ <p>For more information on these and other MPMs, please
+ see the MPM <a href="../mpm.html">documentation</a>.</p>
+
+
+
+ <h3>Atomic Operations</h3>
+
+
+
+ <p>Some modules, such as <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> and
+ recent development builds of the worker MPM, use APR's
+ atomic API. This API provides atomic operations that can
+ be used for lightweight thread synchronization.</p>
+
+ <p>By default, APR implements these operations using the
+ most efficient mechanism available on each target
+ OS/CPU platform. Many modern CPUs, for example, have
+ an instruction that does an atomic compare-and-swap (CAS)
+ operation in hardware. On some platforms, however, APR
+ defaults to a slower, mutex-based implementation of the
+ atomic API in order to ensure compatibility with older
+ CPU models that lack such instructions. If you are
+ building Apache for one of these platforms, and you plan
+ to run only on newer CPUs, you can select a faster atomic
+ implementation at build time by configuring Apache with
+ the <code>--enable-nonportable-atomics</code> option:</p>
+
+ <div class="example"><p><code>
+ ./buildconf<br />
+ ./configure --with-mpm=worker --enable-nonportable-atomics=yes
+ </code></p></div>
+
+ <p>The <code>--enable-nonportable-atomics</code> option is
+ relevant for the following platforms:</p>
+
+ <ul>
+
+ <li>Solaris on SPARC<br />
+ By default, APR uses mutex-based atomics on Solaris/SPARC.
+ If you configure with <code>--enable-nonportable-atomics</code>,
+ however, APR generates code that uses a SPARC v8plus opcode for
+ fast hardware compare-and-swap. If you configure Apache with
+ this option, the atomic operations will be more efficient
+ (allowing for lower CPU utilization and higher concurrency),
+ but the resulting executable will run only on UltraSPARC
+ chips.
+ </li>
+
+ <li>Linux on x86<br />
+ By default, APR uses mutex-based atomics on Linux. If you
+ configure with <code>--enable-nonportable-atomics</code>,
+ however, APR generates code that uses a 486 opcode for fast
+ hardware compare-and-swap. This will result in more efficient
+ atomic operations, but the resulting executable will run only
+ on 486 and later chips (and not on 386).
+ </li>
+
+ </ul>
+
+
+
<h3>mod_status and ExtendedStatus On</h3>
<title>Compile-Time Configuration Issues</title>
+ <section>
+
+ <title>Choosing an MPM</title>
+
+ <p>Apache 2.x supports pluggable concurrency models, called
+ <a href="../mpm.html">Multi-Processing Modules</a> (MPMs).
+ When building Apache, you must choose an MPM to use. There
+ are platform-specific MPMs for some platforms:
+ <module>beos</module>, <module>mpm_netware</module>,
+ <module>mpmt_os2</module>, and <module>mpm_winnt</module>. For
+ general Unix-type systems, there are several MPMs from which
+ to choose. The choice of MPM can affect the speed and scalability
+ of the httpd:</p>
+
+ <ul>
+
+ <li>The <module>worker</module> MPM uses multiple child
+ processes with many threads each. Each thread handles
+ one connection at a time. Worker generally is a good
+ choice for high-traffic servers because it has a smaller
+ memory footprint than the prefork MPM.</li>
+
+ <li>The <module>prefork</module> MPM uses multiple child
+ processes with one thread each. Each process handles
+ one connection at a time. On many systems, prefork is
+ comparable in speed to worker, but it uses more memory.
+ Prefork's threadless design has advantages over worker
+ in some situations: it can be used with non-thread-safe
+ third-party modules, and it is easier to debug on platforms
+ with poor thread debugging support.</li>
+
+ </ul>
+
+ <p>For more information on these and other MPMs, please
+ see the MPM <a href="../mpm.html">documentation</a>.</p>
+
+ </section>
+
+ <section>
+
+ <title>Atomic Operations</title>
+
+ <p>Some modules, such as <module>mod_cache</module> and
+ recent development builds of the worker MPM, use APR's
+ atomic API. This API provides atomic operations that can
+ be used for lightweight thread synchronization.</p>
+
+ <p>By default, APR implements these operations using the
+ most efficient mechanism available on each target
+ OS/CPU platform. Many modern CPUs, for example, have
+ an instruction that does an atomic compare-and-swap (CAS)
+ operation in hardware. On some platforms, however, APR
+ defaults to a slower, mutex-based implementation of the
+ atomic API in order to ensure compatibility with older
+ CPU models that lack such instructions. If you are
+ building Apache for one of these platforms, and you plan
+ to run only on newer CPUs, you can select a faster atomic
+ implementation at build time by configuring Apache with
+ the <code>--enable-nonportable-atomics</code> option:</p>
+
+ <example>
+ ./buildconf<br />
+ ./configure --with-mpm=worker --enable-nonportable-atomics=yes
+ </example>
+
+ <p>The <code>--enable-nonportable-atomics</code> option is
+ relevant for the following platforms:</p>
+
+ <ul>
+
+ <li>Solaris on SPARC<br />
+ By default, APR uses mutex-based atomics on Solaris/SPARC.
+ If you configure with <code>--enable-nonportable-atomics</code>,
+ however, APR generates code that uses a SPARC v8plus opcode for
+ fast hardware compare-and-swap. If you configure Apache with
+ this option, the atomic operations will be more efficient
+ (allowing for lower CPU utilization and higher concurrency),
+ but the resulting executable will run only on UltraSPARC
+ chips.
+ </li>
+
+ <li>Linux on x86<br />
+ By default, APR uses mutex-based atomics on Linux. If you
+ configure with <code>--enable-nonportable-atomics</code>,
+ however, APR generates code that uses a 486 opcode for fast
+ hardware compare-and-swap. This will result in more efficient
+ atomic operations, but the resulting executable will run only
+ on 486 and later chips (and not on 386).
+ </li>
+
+ </ul>
+
+ </section>
+
<section>
<title>mod_status and ExtendedStatus On</title>
projects / apache / commitdiff