.. _cpu:

CPU
===

The CPU stats are shown as a percentage or values and for the configured
refresh time.

The total CPU usage is displayed on the first line.

.. image:: ../_static/cpu.png

If enough horizontal space is available, extended CPU information are
displayed.

.. image:: ../_static/cpu-wide.png

A character is also displayed just after the CPU header and shows the
trend value:

======== ==============================================================
Trend    Status
======== ==============================================================
``-``    CPU value is equal to the mean of the six latests refreshes
``\``    CPU value is lower than the mean of the six latests refreshes
``/``    CPU value is higher than the mean of the six latests refreshes
======== ==============================================================

CPU stats description:

- **user**: percent time spent in user space. User CPU time is the time
  spent on the processor running your program's code (or code in
  libraries).
- **system**: percent time spent in kernel space. System CPU time is the
  time spent running code in the Operating System kernel.
- **idle**: percent of CPU used by any program. Every program or task
  that runs on a computer system occupies a certain amount of processing
  time on the CPU. If the CPU has completed all tasks it is idle.
- **nice** *(\*nix)*: percent time occupied by user level processes with
  a positive nice value. The time the CPU has spent running users'
  processes that have been *niced*.
- **irq** *(Linux, \*BSD)*: percent time spent servicing/handling
  hardware/software interrupts. Time servicing interrupts (hardware +
  software).
- **iowait** *(Linux)*: percent time spent by the CPU waiting for I/O
  operations to complete.
- **steal** *(Linux)*: percentage of time a virtual CPU waits for a real
  CPU while the hypervisor is servicing another virtual processor.
- **ctx_sw**: number of context switches (voluntary + involuntary) per
  second. A context switch is a procedure that a computer's CPU (central
  processing unit) follows to change from one task (or process) to
  another while ensuring that the tasks do not conflict.
- **inter**: number of interrupts per second.
- **sw_inter**: number of software interrupts per second. Always set to
  0 on Windows and SunOS.
- **syscal**: number of system calls per second. Do not displayed on
  Linux (always 0).

To switch to per-CPU stats, just hit the ``1`` key:

.. image:: ../_static/per-cpu.png

By default, ``steal`` CPU time alerts aren't logged. If you want that,
just add to the configuration file:

.. code-block:: ini

    [cpu]
    steal_log=True

Legend:

================= ============
CPU (user/system) Status
================= ============
``<50%``          ``OK``
``>50%``          ``CAREFUL``
``>70%``          ``WARNING``
``>90%``          ``CRITICAL``
================= ============

.. note::
    Limit values can be overwritten in the configuration file under
    the ``[cpu]`` and/or ``[percpu]`` sections.