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<img alt="Erlang logo" src="../../../../doc/erlang-logo.png"><br><small><a href="index.html">Reference Manual</a><br><a href="release_notes.html">Release Notes</a><br><a href="../pdf/os_mon-2.2.10.pdf">PDF</a><br><a href="../../../../doc/index.html">Top</a></small><p><strong>OS_Mon</strong><br><strong>Reference Manual</strong><br><small>Version 2.2.10</small></p>
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<li title="nprocs-0"><a href="cpu_sup.html#nprocs-0">nprocs/0</a></li>
<li title="avg1-0"><a href="cpu_sup.html#avg1-0">avg1/0</a></li>
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<li title="avg15-0"><a href="cpu_sup.html#avg15-0">avg15/0</a></li>
<li title="util-0"><a href="cpu_sup.html#util-0">util/0</a></li>
<li title="util-1"><a href="cpu_sup.html#util-1">util/1</a></li>
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<!-- refpage --><center><h1>cpu_sup</h1></center>
<h3>MODULE</h3>
<div class="REFBODY">cpu_sup</div>
<h3>MODULE SUMMARY</h3>
<div class="REFBODY">A CPU Load and CPU Utilization Supervisor Process</div>
<h3>DESCRIPTION</h3>
<div class="REFBODY"><p>
<p><span class="code">cpu_sup</span> is a process which supervises the CPU load
and CPU utilization. It is part of the OS_Mon application, see
<span class="bold_code"><a href="os_mon_app.html">os_mon(6)</a></span>. Available for Unix,
although CPU utilization values (<span class="code">util/0,1</span>) are only
available for Solaris and Linux.</p>
<p>The load values are proportional to how long time a runnable
Unix process has to spend in the run queue before it is scheduled.
Accordingly, higher values mean more system load. The returned
value divided by 256 produces the figure displayed by <span class="code">rup</span>
and <span class="code">top</span>. What is displayed as 2.00 in <span class="code">rup</span>, is
displayed as load up to the second mark in <span class="code">xload</span>.</p>
<p>For example, <span class="code">rup</span> displays a load of 128 as 0.50, and
512 as 2.00.</p>
<p>If the user wants to view load values as percentage of machine
capacity, then this way of measuring presents a problem, because
the load values are not restricted to a fixed interval. In this
case, the following simple mathematical transformation can
produce the load value as a percentage:</p>
<div class="example"><pre>
PercentLoad = 100 * (1 - D/(D + Load))
</pre></div>
<p><span class="code">D</span> determines which load value should be associated with
which percentage. Choosing <span class="code">D</span> = 50 means that 128 is 60%
load, 256 is 80%, 512 is 90%, and so on.</p>
<p>Another way of measuring system load is to divide the number of
busy CPU cycles by the total number of CPU cycles. This produces
values in the 0-100 range immediately. However, this method hides
the fact that a machine can be more or less saturated. CPU
utilization is therefore a better name than system load for this
measure.</p>
<p>A server which receives just enough requests to never become
idle will score a CPU utilization of 100%. If the server receives
50% more requests, it will still scores 100%. When the system load
is calculated with the percentage formula shown previously,
the load will increase from 80% to 87%.</p>
<p>The <span class="code">avg1/0</span>, <span class="code">avg5/0</span>, and <span class="code">avg15/0</span> functions
can be used for retrieving system load values, and
the <span class="code">util/0</span> and <span class="code">util/1</span> functions can be used for
retrieving CPU utilization values.</p>
<p>When run on Linux, <span class="code">cpu_sup</span> assumes that the <span class="code">/proc</span>
file system is present and accessible by <span class="code">cpu_sup</span>. If it is
not, <span class="code">cpu_sup</span> will terminate.</p>
</p></div>
<h3>EXPORTS</h3>
<p><a name="nprocs-0"><span class="bold_code">nprocs() -> UnixProcesses | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">UnixProcesses = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the number of UNIX processes running on this machine.
This is a crude way of measuring the system load, but it may
be of interest in some cases.</p>
<p>Returns 0 if <span class="code">cpu_sup</span> is not available.</p>
</p></div>
<p><a name="avg1-0"><span class="bold_code">avg1() -> SystemLoad | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">SystemLoad = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the average system load in the last minute, as
described above. 0 represents no load, 256 represents the load
reported as 1.00 by <span class="code">rup</span>.</p>
<p>Returns 0 if <span class="code">cpu_sup</span> is not available.</p>
</p></div>
<p><a name="avg5-0"><span class="bold_code">avg5() -> SystemLoad | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">SystemLoad = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the average system load in the last five minutes, as
described above. 0 represents no load, 256 represents the load
reported as 1.00 by <span class="code">rup</span>.</p>
<p>Returns 0 if <span class="code">cpu_sup</span> is not available.</p>
</p></div>
<p><a name="avg15-0"><span class="bold_code">avg15() -> SystemLoad | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">SystemLoad = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns the average system load in the last 15 minutes, as
described above. 0 represents no load, 256 represents the load
reported as 1.00 by <span class="code">rup</span>.</p>
<p>Returns 0 if <span class="code">cpu_sup</span> is not available.</p>
</p></div>
<p><a name="util-0"><span class="bold_code">util() -> CpuUtil | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">CpuUtil = float()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns CPU utilization since the last call to
<span class="code">util/0</span> or <span class="code">util/1</span> by the calling process.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The returned value of the first call to <span class="code">util/0</span> or
<span class="code">util/1</span> by a process will on most systems be the CPU
utilization since system boot, but this is not guaranteed
and the value should therefore be regarded as garbage. This
also applies to the first call after a restart of
<span class="code">cpu_sup</span>.</p>
</p></div>
</div>
<p>The CPU utilization is defined as the sum of the percentage
shares of the CPU cycles spent in all busy processor states
(see <span class="code">util/1</span> below) in average on all CPUs.</p>
<p>Returns 0 if <span class="code">cpu_sup</span> is not available.</p>
</p></div>
<p><a name="util-1"><span class="bold_code">util(Opts) -> UtilSpec | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Opts = [detailed | per_cpu]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">UtilSpec = UtilDesc | [UtilDesc]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> UtilDesc = {Cpus, Busy, NonBusy, Misc}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Cpus = all | int() | [int()]()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Busy = NonBusy = {State, Share} | Share</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> State = user | nice_user | kernel</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> | wait | idle | atom()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Share = float()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Misc = []</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns CPU utilization since the last call to
<span class="code">util/0</span> or <span class="code">util/1</span> by the calling process, in
more detail than <span class="code">util/0</span>.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The returned value of the first call to <span class="code">util/0</span> or
<span class="code">util/1</span> by a process will on most systems be the CPU
utilization since system boot, but this is not guaranteed
and the value should therefore be regarded as garbage. This
also applies to the first call after a restart of
<span class="code">cpu_sup</span>.</p>
</p></div>
</div>
<p>Currently recognized options:</p>
<dl>
<dt><strong><span class="code">detailed</span></strong></dt>
<dd>
<p>The returned <span class="code">UtilDesc</span>(s) will be even more
detailed.</p>
</dd>
<dt><strong><span class="code">per_cpu</span></strong></dt>
<dd>
<p>Each CPU will be specified separately (assuming this
information can be retrieved from the operating system),
that is, a list with one <span class="code">UtilDesc</span> per CPU will be
returned.</p>
</dd>
</dl>
<p>Description of <span class="code">UtilDesc = {Cpus, Busy, NonBusy, Misc}</span>:</p>
<dl>
<dt><strong><span class="code">Cpus</span></strong></dt>
<dd>
<p>If the <span class="code">detailed</span> and/or <span class="code">per_cpu</span> option is
given, this is the CPU number, or a list of the CPU
numbers.</p>
<p>If not, this is the atom <span class="code">all</span> which implies that
the <span class="code">UtilDesc</span> contains information about all CPUs.</p>
</dd>
<dt><strong><span class="code">Busy</span></strong></dt>
<dd>
<p>If the <span class="code">detailed</span> option is given, this is a list
of <span class="code">{State, Share}</span> tuples, where each tuple
contains information about a processor state that has
been identified as a busy processor state (see below).
The atom <span class="code">State</span> is the name of the state, and
the float <span class="code">Share</span> represents the percentage share of
the CPU cycles spent in this state since the last call to
<span class="code">util/0</span> or <span class="code">util/1</span>.</p>
<p>If not, this is the sum of the percentage shares of
the CPU cycles spent in all states identified as busy.</p>
<p>If the <span class="code">per_cpu</span> is not given, the value(s)
presented are the average of all CPUs.</p>
</dd>
<dt><strong><span class="code">NonBusy</span></strong></dt>
<dd>
<p>Similar to <span class="code">Busy</span>, but for processor states that
have been identified as non-busy (see below).</p>
</dd>
<dt><strong><span class="code">Misc</span></strong></dt>
<dd>
<p>Currently unused; reserved for future use.</p>
</dd>
</dl>
<p>Currently these processor states are identified as busy:</p>
<dl>
<dt><strong><span class="code">user</span></strong></dt>
<dd>
<p>Executing code in user mode.</p>
</dd>
<dt><strong><span class="code">nice_user</span></strong></dt>
<dd>
<p>Executing code in low priority (nice) user mode.
This state is currently only identified on Linux.</p>
</dd>
<dt><strong><span class="code">kernel</span></strong></dt>
<dd>
<p>Executing code in kernel mode.</p>
</dd>
</dl>
<p>Currently these processor states are identified as non-busy:</p>
<dl>
<dt><strong><span class="code">wait</span></strong></dt>
<dd>
<p>Waiting. This state is currently only identified on
Solaris.</p>
</dd>
<dt><strong><span class="code">idle</span></strong></dt>
<dd>
<p>Idle.</p>
</dd>
</dl>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>Identified processor states may be different on different
operating systems and may change between different versions
of <span class="code">cpu_sup</span> on the same operating system. The sum of
the percentage shares of the CPU cycles spent in all busy
and all non-busy processor states will always add up to
100%, though.</p>
</p></div>
</div>
<p>Returns <span class="code">{all,0,0,[]}</span> if <span class="code">cpu_sup</span> is not
available.</p>
</p></div>
<h3><a name="id63414">See Also</a></h3>
<div class="REFBODY">
<p><span class="bold_code"><a href="os_mon_app.html">os_mon(3)</a></span></p>
</div>
</div>
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<p>Copyright © 1997-2012 Ericsson AB. All Rights Reserved.</p>
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