forked from lijiext/lammps
80 lines
3.1 KiB
HTML
80 lines
3.1 KiB
HTML
<HTML>
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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</CENTER>
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<HR>
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<H3>timer command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>timer args
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</PRE>
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<LI><I>args</I> = one or more of <I>off</I> or <I>loop</I> or <I>normal</I> or <I>full</I> or <I>sync</I> or <I>nosync</I>
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<PRE> <I>off</I> = do not collect or print any timing information
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<I>loop</I> = collect only the total time for the simulation loop
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<I>normal</I> = collect timer information broken down by sections (default)
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<I>full</I> = like <I>normal</I> but also include CPU and thread utilzation
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<I>sync</I> = explicitly synchronize MPI tasks between sections
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<I>nosync</I> = do not synchronize MPI tasks between sections (default)
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>timer full sync
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timer loop
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Select the level of detail LAMMPS performs its CPU timings.
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</P>
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<P>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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<A HREF = "Section_start.html#start_8">discussion of screen output</A>.
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</P>
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<P>The <I>off</I> setting will turn all time measurements off. The <I>loop</I>
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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 <I>normal</I> 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 <I>full</I> setting adds information about CPU
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utilization and thread utilization, when multi-threading is enabled.
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</P>
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<P>With the <I>sync</I> 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 <I>nosync</I> setting (which is the
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default) turns off this synchronization.
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</P>
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<P>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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</P>
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<P>IMPORTANT NOTE: Using the <I>full</I> and <I>sync</I> options provides the most
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detailed 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 <I>normal</I> setting
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can have a measurable negative performance impact. In those cases you
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can just use the <I>loop</I> or <I>off</I> setting.
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</P>
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<P><B>Restrictions:</B> none
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "run.html">run post no</A>, <A HREF = "kspace_modify.html">kspace_modify fftbench</A>
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</P>
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<P><B>Default:</B>
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</P>
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<P>timer normal nosync
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</P>
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</HTML>
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