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timer.txt
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.. 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*
.. 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)
Examples
""""""""
.. parsed-literal::
timer full sync
timer loop
Description
"""""""""""
Select the level of detail 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
valuable 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.
Multiple keywords can be specified. 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
"""""""
timer normal nosync
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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