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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@13938 f3b2605a-c512-4ea7-a41b-209d697bcdaa
78 lines
3.1 KiB
HTML
78 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>timestep command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>timers 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 and print 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 in 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 when collecting timer info (default)
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>timers full sync
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timers 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 to which level of detail LAMMPS is performing internal profiling.
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</P>
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<P>During regular runs LAMMPS will collect information about how much time is
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spent in different sections of the code and thus can provide valuable
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information for determining performance and load imbalance problems. This
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can be done at different levels of detail and accuracy. For more
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information about the timing output, please have a look at the <A HREF = "Section_start.html#start_8">discussion
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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> setting
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will only measure the total time of run loop and not collect any detailed
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per section information. With the <I>normal</I> setting, timing information for
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individual sections of the code are collected and also information about
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load imbalances inside those sections presented. The <I>full</I> setting adds
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information about CPU utilization and thread utilization, when multi-threading
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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 call
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and thus allowing to study load imbalance more accuractly, but this usually
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has some performance impact. Using the <I>nosync</I> setting this can be turned
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off (which is the default).
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</P>
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<P>Multiple keywords can be provided and for keywords that are mutually
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exclusive, the last one in that group is taking 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 also can have a significant
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negative 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 making tests
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to identify the performance. For calculations with few atoms or a very
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large number of performance, even using the <I>normal</I> setting can have
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a measurable performance impact. It is recommended in those cases to use
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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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<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>timers normal nosync
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</P>
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</HTML>
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