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<?xml version="1.0" encoding="latin1" ?>
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<!DOCTYPE erlref SYSTEM "erlref.dtd">
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<holder>Ericsson AB, All Rights Reserved</holder>
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The contents of this file are subject to the Erlang Public License,
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Version 1.1, (the "License"); you may not use this file except in
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compliance with the License. You should have received a copy of the
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Erlang Public License along with this software. If not, it can be
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retrieved online at http://www.erlang.org/.
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Software distributed under the License is distributed on an "AS IS"
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basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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the License for the specific language governing rights and limitations
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The Initial Developer of the Original Code is Ericsson AB.
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<title>cpu_sup</title>
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<module>cpu_sup</module>
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<modulesummary>A CPU Load and CPU Utilization Supervisor Process</modulesummary>
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<p><c>cpu_sup</c> is a process which supervises the CPU load
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and CPU utilization. It is part of the OS_Mon application, see
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<seealso marker="os_mon">os_mon(6)</seealso>. Available for Unix,
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although CPU utilization values (<c>util/0,1</c>) are only
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available for Solaris and Linux.</p>
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<p>The load values are proportional to how long time a runnable
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Unix process has to spend in the run queue before it is scheduled.
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Accordingly, higher values mean more system load. The returned
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value divided by 256 produces the figure displayed by <c>rup</c>
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and <c>top</c>. What is displayed as 2.00 in <c>rup</c>, is
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displayed as load up to the second mark in <c>xload</c>.</p>
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<p>For example, <c>rup</c> displays a load of 128 as 0.50, and
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<p>If the user wants to view load values as percentage of machine
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capacity, then this way of measuring presents a problem, because
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the load values are not restricted to a fixed interval. In this
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case, the following simple mathematical transformation can
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produce the load value as a percentage:</p>
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PercentLoad = 100 * (1 - D/(D + Load))
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<p><c>D</c> determines which load value should be associated with
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which percentage. Choosing <c>D</c> = 50 means that 128 is 60%
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load, 256 is 80%, 512 is 90%, and so on.</p>
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<p>Another way of measuring system load is to divide the number of
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busy CPU cycles by the total number of CPU cycles. This produces
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values in the 0-100 range immediately. However, this method hides
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the fact that a machine can be more or less saturated. CPU
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utilization is therefore a better name than system load for this
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<p>A server which receives just enough requests to never become
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idle will score a CPU utilization of 100%. If the server receives
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50% more requests, it will still scores 100%. When the system load
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is calculated with the percentage formula shown previously,
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the load will increase from 80% to 87%.</p>
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<p>The <c>avg1/0</c>, <c>avg5/0</c>, and <c>avg15/0</c> functions
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can be used for retrieving system load values, and
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the <c>util/0</c> and <c>util/1</c> functions can be used for
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retrieving CPU utilization values.</p>
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<p>When run on Linux, <c>cpu_sup</c> assumes that the <c>/proc</c>
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file system is present and accessible by <c>cpu_sup</c>. If it is
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not, <c>cpu_sup</c> will terminate.</p>
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<name>nprocs() -> UnixProcesses | {error, Reason}</name>
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<fsummary>Get the number of UNIX processes running on this host</fsummary>
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<v>UnixProcesses = int()</v>
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<v>Reason = term()</v>
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<p>Returns the number of UNIX processes running on this machine.
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This is a crude way of measuring the system load, but it may
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be of interest in some cases.</p>
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<p>Returns 0 if <c>cpu_sup</c> is not available.</p>
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<name>avg1() -> SystemLoad | {error, Reason}</name>
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<fsummary>Get the system load average for the last minute</fsummary>
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<v>SystemLoad = int()</v>
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<v>Reason = term()</v>
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<p>Returns the average system load in the last minute, as
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described above. 0 represents no load, 256 represents the load
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reported as 1.00 by <c>rup</c>.</p>
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<p>Returns 0 if <c>cpu_sup</c> is not available.</p>
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<name>avg5() -> SystemLoad | {error, Reason}</name>
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<fsummary>Get the system load average for the last five minutes</fsummary>
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<v>SystemLoad = int()</v>
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<v>Reason = term()</v>
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<p>Returns the average system load in the last five minutes, as
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described above. 0 represents no load, 256 represents the load
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reported as 1.00 by <c>rup</c>.</p>
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<p>Returns 0 if <c>cpu_sup</c> is not available.</p>
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<name>avg15() -> SystemLoad | {error, Reason}</name>
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<fsummary>Get the system load average for the last fifteen minutes</fsummary>
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<v>SystemLoad = int()</v>
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<v>Reason = term()</v>
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<p>Returns the average system load in the last 15 minutes, as
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described above. 0 represents no load, 256 represents the load
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reported as 1.00 by <c>rup</c>.</p>
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<p>Returns 0 if <c>cpu_sup</c> is not available.</p>
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<name>util() -> CpuUtil | {error, Reason}</name>
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<fsummary>Get the CPU utilization</fsummary>
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<v>CpuUtil = float()</v>
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<v>Reason = term()</v>
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<p>Returns CPU utilization since the last call to
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<c>util/0</c> or <c>util/1</c> by the calling process.</p>
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<p>The returned value of the first call to <c>util/0</c> or
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<c>util/1</c> by a process will on most systems be the CPU
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utilization since system boot, but this is not guaranteed
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and the value should therefore be regarded as garbage. This
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also applies to the first call after a restart of
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<p>The CPU utilization is defined as the sum of the percentage
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shares of the CPU cycles spent in all busy processor states
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(see <c>util/1</c> below) in average on all CPUs.</p>
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<p>Returns 0 if <c>cpu_sup</c> is not available.</p>
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<name>util(Opts) -> UtilSpec | {error, Reason}</name>
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<fsummary>Get the CPU utilization</fsummary>
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<v>Opts = [detailed | per_cpu]</v>
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<v>UtilSpec = UtilDesc | [UtilDesc]</v>
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<v> UtilDesc = {Cpus, Busy, NonBusy, Misc}</v>
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<v> Cpus = all | int() | [int()]()</v>
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<v> Busy = NonBusy = {State, Share} | Share</v>
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<v> State = user | nice_user | kernel</v>
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<v> | wait | idle | atom()</v>
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<v> Share = float()</v>
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<v> Misc = []</v>
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<v>Reason = term()</v>
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<p>Returns CPU utilization since the last call to
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<c>util/0</c> or <c>util/1</c> by the calling process, in
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more detail than <c>util/0</c>.</p>
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<p>The returned value of the first call to <c>util/0</c> or
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<c>util/1</c> by a process will on most systems be the CPU
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utilization since system boot, but this is not guaranteed
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and the value should therefore be regarded as garbage. This
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also applies to the first call after a restart of
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<p>Currently recognized options:</p>
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<tag><c>detailed</c></tag>
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<p>The returned <c>UtilDesc</c>(s) will be even more
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<tag><c>per_cpu</c></tag>
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<p>Each CPU will be specified separately (assuming this
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information can be retrieved from the operating system),
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that is, a list with one <c>UtilDesc</c> per CPU will be
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<p>Description of <c>UtilDesc = {Cpus, Busy, NonBusy, Misc}</c>:</p>
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<tag><c>Cpus</c></tag>
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<p>If the <c>detailed</c> and/or <c>per_cpu</c> option is
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given, this is the CPU number, or a list of the CPU
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<p>If not, this is the atom <c>all</c> which implies that
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the <c>UtilDesc</c> contains information about all CPUs.</p>
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<tag><c>Busy</c></tag>
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<p>If the <c>detailed</c> option is given, this is a list
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of <c>{State, Share}</c> tuples, where each tuple
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contains information about a processor state that has
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been identified as a busy processor state (see below).
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The atom <c>State</c> is the name of the state, and
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the float <c>Share</c> represents the percentage share of
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the CPU cycles spent in this state since the last call to
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<c>util/0</c> or <c>util/1</c>.</p>
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<p>If not, this is the sum of the percentage shares of
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the CPU cycles spent in all states identified as busy.</p>
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<p>If the <c>per_cpu</c> is not given, the value(s)
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presented are the average of all CPUs.</p>
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<tag><c>NonBusy</c></tag>
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<p>Similar to <c>Busy</c>, but for processor states that
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have been identified as non-busy (see below).</p>
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<tag><c>Misc</c></tag>
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<p>Currently unused; reserved for future use.</p>
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<p>Currently these processor states are identified as busy:</p>
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<tag><c>user</c></tag>
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<p>Executing code in user mode.</p>
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<tag><c>nice_user</c></tag>
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<p>Executing code in low priority (nice) user mode.
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This state is currently only identified on Linux.</p>
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<tag><c>kernel</c></tag>
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<p>Executing code in kernel mode.</p>
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<p>Currently these processor states are identified as non-busy:</p>
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<tag><c>wait</c></tag>
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<p>Waiting. This state is currently only identified on
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<tag><c>idle</c></tag>
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<p>Identified processor states may be different on different
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operating systems and may change between different versions
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of <c>cpu_sup</c> on the same operating system. The sum of
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the percentage shares of the CPU cycles spent in all busy
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and all non-busy processor states will always add up to
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<p>Returns <c>{all,0,0,[]}</c> if <c>cpu_sup</c> is not
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<title>See Also</title>
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<p><seealso marker="os_mon">os_mon(3)</seealso></p>
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lib/os_mon/doc/src/cpu_sup.xml
