Drazen Urch
7bd1550195
* Checkpoint * cpu cycle ffi * Rename * mixnode feature * Bundle libcpucycles
92 lines
4.0 KiB
HTML
92 lines
4.0 KiB
HTML
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<title>
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API</title>
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<div class=headline>
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libcpucycles
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</div>
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<div class=nav>
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<div class="navt away"><a href=index.html>Intro</a>
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</div><div class="navt away"><a href=download.html>Download</a>
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</div><div class="navt away"><a href=install.html>Install</a>
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</div><div class="navt here">API
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</div><div class="navt away"><a href=counters.html>Counters</a>
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</div><div class="navt away"><a href=selection.html>Selection</a>
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</div><div class="navt away"><a href=security.html>Security</a>
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</div></div>
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<div class=main>
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<h3>NAME</h3>
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<p>cpucycles - count CPU cycles</p>
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<h3>SYNOPSIS</h3>
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<pre><code>#include <cpucycles.h>
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long long count = cpucycles();
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long long persecond = cpucycles_persecond();
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const char *implementation = cpucycles_implementation();
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const char *version = cpucycles_version();
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</code></pre>
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<p>Link with <code>-lcpucycles</code>. Old systems may also need <code>-lrt</code>.</p>
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<h3>DESCRIPTION</h3>
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<p><code>cpucycles()</code> returns an estimate for the number of CPU cycles that have
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occurred since an unspecified time in the past (perhaps system boot,
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perhaps program startup).</p>
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<p>Accessing true cycle counters can be difficult on some CPUs and
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operating systems. <code>cpucycles()</code> does its best to produce accurate
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results, but selects a low-precision counter if the only other option is
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failure.</p>
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<p><code>cpucycles_persecond()</code> returns an estimate for the number of CPU cycles
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per second. This estimate comes from <code>/etc/cpucyclespersecond</code> if that
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file exists, otherwise from various OS mechanisms, otherwise from the
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<code>cpucyclespersecond</code> environment variable if that is set, otherwise
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2399987654.</p>
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<p><code>cpucycles_implementation()</code> returns the name of the counter in use:
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e.g., <code>"amd64-pmc"</code>.</p>
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<p><code>cpucycles_version()</code> returns the <code>libcpucycles</code> version number as a
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string: e.g., <code>"20230115"</code>. Results of <code>cpucycles_implementation()</code>
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should be interpreted relative to <code>cpucycles_version()</code>.</p>
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<p><code>cpucycles</code> is actually a function pointer. The first call to
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<code>cpucycles()</code> or <code>cpucycles_persecond()</code> or <code>cpucycles_implementation()</code>
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selects one of the available counters and updates the <code>cpucycles</code>
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pointer accordingly. Subsequent calls to <code>cpucycles()</code> are thread-safe.</p>
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<h3>SEE ALSO</h3>
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<p><strong>gettimeofday</strong>(2), <strong>clock_gettime</strong>(2)</p><hr><font size=1><b>Version:</b>
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This is version 2023.01.15 of the "API" web page.
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</font>
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