.. index:: timer

timer command
=============

Syntax
""""""

.. parsed-literal::

   timer args

* *args* = one or more of *off* or *loop* or *normal* or *full* or *sync* or *nosync* or *timeout* or *every*
.. parsed-literal::

     *off* = do not collect or print any timing information
     *loop* = collect only the total time for the simulation loop
     *normal* = collect timer information broken down by sections (default)
     *full* = like *normal* but also include CPU and thread utilzation 
     *sync* = explicitly synchronize MPI tasks between sections
     *nosync* = do not synchronize MPI tasks between sections (default)
     *timeout* elapse = set walltime limit to *elapse*
     *every* Ncheck = perform timeout check every *Ncheck* steps

Examples
""""""""

.. parsed-literal::

   timer full sync
   timer timeout 2:00:00 every 100
   timer loop

Description
"""""""""""

Select the level of detail at which LAMMPS performs its CPU timings.

During a simulation run LAMMPS collects information about how much
time is spent in different sections of the code and thus can provide
information for determining performance and load imbalance problems.
This can be done at different levels of detail and accuracy.  For more
information about the timing output, see this :ref:`discussion of screen output <start_8>`.

The *off* setting will turn all time measurements off. The *loop*
setting will only measure the total time for a run and not collect any
detailed per section information.  With the *normal* setting, timing
information for portions of the timestep (pairwise calculations,
neighbor list construction, output, etc) are collected as well as
information about load imbalances for those sections across
procsessors.  The *full* setting adds information about CPU
utilization and thread utilization, when multi-threading is enabled.

With the *sync* setting, all MPI tasks are synchronized at each timer
call which meaures load imbalance more accuractly, though it can also
slow down the simulation.  Using the *nosync* setting (which is the
default) turns off this synchronization.

With the *timeout* keyword a walltime limit can be imposed that
affects the :doc:`run <run>` and :doc:`minimize <minimize>` commands.  If
the time limit is reached, the run or energy minimization will exit on
the next step or iteration that is a multiple of the *Ncheck* value
specified with the *every* keyword.  All subsequent run or minimize
commands in the input script will be skipped until the timeout is
reset or turned off by a new *timer* command.  The timeout *elapse*
value can be specified as *off* or *unlimited* to impose no timeout
condition (which is the default).  The *elapse* setting can be
specified as a single number for seconds, two numbers separated by a
colon (MM:SS) for minutes and seconds, or as three numbers separated
by colons for hours, minutes, and seconds.

The *every* keyword sets how frequently during a run or energy
minimization the wall clock will be checked.  This check count applies
to the outer iterations or time steps during minimizations or :doc:`r-RESPA runs <run_style>`, respectively.  Checking for timeout too often,
can slow a calculation down.  Checking too infrequently can make the
timeout measurement less accurate, with the run being stopped later
than desired.

Multiple keywords can be specified with the *timer* command.  For
keywords that are mutually exclusive, the last one specified takes
effect.

.. note::

   Using the *full* and *sync* options provides the most detailed
   and accurate timing information, but can also have a negative
   performance impact due to the overhead of the many required system
   calls. It is thus recommended to use these settings only when testing
   tests to identify performance bottlenecks. For calculations with few
   atoms or a very large number of processors, even the *normal* setting
   can have a measurable negative performance impact. In those cases you
   can just use the *loop* or *off* setting.

Restrictions
""""""""""""
 none

Related commands
""""""""""""""""

:doc:`run post no <run>`, :doc:`kspace_modify fftbench <kspace_modify>`

Default
"""""""

.. parsed-literal::

   timer normal nosync
   timer timeout off
   timer every 10


.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm