forked from lijiext/lammps
89 lines
2.8 KiB
Plaintext
89 lines
2.8 KiB
Plaintext
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.. index:: timer
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timer command
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=============
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Syntax
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""""""
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.. parsed-literal::
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timer args
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* *args* = one or more of *off* or *loop* or *normal* or *full* or *sync* or *nosync*
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.. parsed-literal::
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*off* = do not collect or print any timing information
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*loop* = collect only the total time for the simulation loop
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*normal* = collect timer information broken down by sections (default)
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*full* = like *normal* but also include CPU and thread utilzation
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*sync* = explicitly synchronize MPI tasks between sections
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*nosync* = do not synchronize MPI tasks between sections (default)
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Examples
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""""""""
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.. parsed-literal::
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timer full sync
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timer loop
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Description
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"""""""""""
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Select the level of detail LAMMPS performs its CPU timings.
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During a simulation run LAMMPS collects information about how much
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time is spent in different sections of the code and thus can provide
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valuable information for determining performance and load imbalance
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problems. This can be done at different levels of detail and
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accuracy. For more information about the timing output, see this
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:ref:`discussion of screen output <start_8>`.
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The *off* setting will turn all time measurements off. The *loop*
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setting will only measure the total time for a run and not collect any
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detailed per section information. With the *normal* setting, timing
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information for portions of the timestep (pairwise calculations,
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neighbor list construction, output, etc) are collected as well as
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information about load imbalances for those sections across
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procsessors. The *full* setting adds information about CPU
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utilization and thread utilization, when multi-threading is enabled.
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With the *sync* setting, all MPI tasks are synchronized at each timer
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call which meaures load imbalance more accuractly, though it can also
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slow down the simulation. Using the *nosync* setting (which is the
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default) turns off this synchronization.
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Multiple keywords can be specified. For keywords that are mutually
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exclusive, the last one specified takes effect.
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.. note::
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Using the *full* and *sync* options provides the most detailed
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and accurate timing information, but can also have a negative
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performance impact due to the overhead of the many required system
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calls. It is thus recommended to use these settings only when testing
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tests to identify performance bottlenecks. For calculations with few
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atoms or a very large number of processors, even the *normal* setting
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can have a measurable negative performance impact. In those cases you
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can just use the *loop* or *off* setting.
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Restrictions
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""""""""""""
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none
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Related commands
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""""""""""""""""
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:doc:`run post no <run>`, :doc:`kspace_modify fftbench <kspace_modify>`
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Default
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"""""""
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timer normal nosync
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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