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<html> <head> <meta http-equiv="content-type" content="text/html; charset=utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <style type="text/css"> html{overflow-y:scroll} body{font-family:sans-serif} p,ul,ol,blockquote,pre{font-size:0.9em;line-height:1.6em} li p{font-size:1.0em} blockquote p{font-size:1.0em} tt{font-size:1.2em} code{font-size:1.2em} h1{font-size:1.5em} h2{font-size:1.3em} h3{font-size:1.0em} h1 a{text-decoration:none} table{border-collapse:collapse} th,td{border:1px solid black} table a{text-decoration:none} table tr{font-size:0.9em;line-height:1.6em} .links a:hover{text-decoration:underline} .links a:active{text-decoration:underline} .links img{width:200px;padding-left:1em} .links td{border:0px;padding-top:0.5em;padding-bottom:0.5em} .headline{padding:0;font-weight:bold;font-size:1.5em;vertical-align:top;padding-bottom:0.5em;color:#125d0d} .navt{display:inline-block;box-sizing:border-box;-moz-box-sizing:border-box;-webkit-box-sizing:border-box; min-width:14%;margin:0;padding:0;padding-left:0.5em;padding-right:0.5em;vertical-align:center; font-weight:bold;font-size:1.1em;text-align:center;border:1px solid black} .here{border-bottom:0px;background-color:#ffffff} .away{background-color:#125d0d;} .away a{text-decoration:none;display:block;color:#ffffff} .away a:hover,.away a:active{text-decoration:underline} .main{margin:0;padding-top:0em;padding-bottom:1%;clear:both} </style> <title> API</title> </head> <body> <div class=headline> libcpucycles </div> <div class=nav> <div class="navt away"><a href=index.html>Intro</a> </div><div class="navt away"><a href=download.html>Download</a> </div><div class="navt away"><a href=install.html>Install</a> </div><div class="navt here">API </div><div class="navt away"><a href=counters.html>Counters</a> </div><div class="navt away"><a href=selection.html>Selection</a> </div><div class="navt away"><a href=security.html>Security</a> </div></div> <div class=main> <h3>NAME</h3> <p>cpucycles - count CPU cycles</p> <h3>SYNOPSIS</h3> <pre><code>#include &lt;cpucycles.h&gt; long long count = cpucycles(); long long persecond = cpucycles_persecond(); const char *implementation = cpucycles_implementation(); </code></pre> <p>Link with <code>-lcpucycles</code>. Old systems may also need <code>-lrt</code>.</p> <h3>DESCRIPTION</h3> <p><code>cpucycles()</code> returns an estimate for the number of CPU cycles that have occurred since an unspecified time in the past (perhaps system boot, perhaps program startup).</p> <p>Accessing true cycle counters can be difficult on some CPUs and operating systems. <code>cpucycles()</code> does its best to produce accurate results, but selects a low-precision counter if the only other option is failure.</p> <p><code>cpucycles_persecond()</code> returns an estimate for the number of CPU cycles per second. This estimate comes from <code>/etc/cpucyclespersecond</code> if that file exists, otherwise from various OS mechanisms, otherwise from the <code>cpucyclespersecond</code> environment variable if that is set, otherwise 1000000000.</p> <p><code>cpucycles_implementation()</code> returns the name of the counter in use: e.g., <code>"amd64-pmc"</code>.</p> <p><code>cpucycles</code> is actually a function pointer. The first call to <code>cpucycles()</code> or <code>cpucycles_persecond()</code> or <code>cpucycles_implementation()</code> selects one of the available counters and updates the <code>cpucycles</code> pointer accordingly. Subsequent calls to <code>cpucycles()</code> are thread-safe.</p> <h3>SEE ALSO</h3> <p><strong>gettimeofday</strong>(2), <strong>clock_gettime</strong>(2)</p><hr><font size=1><b>Version:</b> This is version 2023.01.05 of the "API" web page. </font> </div> </body> </html>