forked from lijiext/lammps
113 lines
4.4 KiB
HTML
113 lines
4.4 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>fix gpu command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID gpu mode first last split
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>gpu = style name of this fix command
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<LI>mode = force or force/neigh
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<LI>first = ID of first GPU to be used on each node
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<LI>last = ID of last GPU to be used on each node
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<LI>split = fraction of particles assigned to the GPU
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>fix 0 all gpu force 0 0 1.0
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fix 0 all gpu force 0 0 0.75
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fix 0 all gpu force/neigh 0 0 1.0
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fix 0 all gpu force/neigh 0 1 -1.0
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Select and initialize GPUs to be used for acceleration and configure
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GPU acceleration in LAMMPS. This fix is required in order to use
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any style with GPU acceleration. The fix must be the first fix
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specified for a run or an error will be generated. The fix will not have an
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effect on any LAMMPS computations that do not use GPU acceleration, so there
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should not be any problems with specifying this fix first in input scripts.
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</P>
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<P>The <I>mode</I> setting specifies where neighbor list calculations will be
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performed. If <I>mode</I> is force, neighbor list calculation is performed
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on the CPU. If <I>mode</I> is force/neigh, neighbor list calculation is
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performed on the GPU. GPU neighbor list calculation currently cannot
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be used with a triclinic box. GPU neighbor list calculation currently
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cannot be used with <A HREF = "pair_hybrid.html">hybrid</A> pair styles. GPU
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neighbor lists are not compatible with styles that are not
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GPU-enabled. When a non-GPU enabled style requires a neighbor list,
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it will also be built using CPU routines. In these cases, it will
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typically be more efficient to only use CPU neighbor list builds.
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</P>
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<P>The <I>first</I> and <I>last</I> settings specify the GPUs that will be used for
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simulation. On each node, the GPU IDs in the inclusive range from
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<I>first</I> to <I>last</I> will be used.
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</P>
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<P>The <I>split</I> setting can be used for load balancing force calculation
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work between CPU and GPU cores in GPU-enabled pair styles. If
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0<<I>split</I><1.0, a fixed fraction of particles is offloaded to the GPU
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while force calculation for the other particles occurs simulataneously
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on the CPU. If <I>split</I><0, the optimal fraction (based on CPU and GPU
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timings) is calculated every 25 timesteps. If <I>split</I>=1.0, all force
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calculations for GPU accelerated pair styles are performed on the
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GPU. In this case, <A HREF = "pair_hybrid.html">hybrid</A>, <A HREF = "bond_style.html">bond</A>,
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<A HREF = "angle_style.html">angle</A>, <A HREF = "dihedral_style.html">dihedral</A>,
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<A HREF = "improper_style.html">improper</A>, and <A HREF = "kspace_style.html">long-range</A>
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calculations can be performed on the CPU while the GPU is performing
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force calculations for the GPU-enabled pair style.
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</P>
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<P>In order to use GPU acceleration, a GPU enabled style must be selected
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in the input script in addition to this fix. Currently, this is
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limited to a few <A HREF = "pair_style.html">pair styles</A> and the PPPM <A HREF = "kspace_style.html">kspace
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style</A>.
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</P>
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<P>See <A HREF = "doc/Section_accerate.html">this section</A> of the manual for more
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details about using the GPU package.
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</P>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>This fix is part of the "gpu" package. It is only enabled if LAMMPS
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was built with that package. See the <A HREF = "Section_start.html#2_3">Making
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LAMMPS</A> section for more info.
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</P>
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<P>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
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are relevant to this fix.
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</P>
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<P>No parameter of this fix can be used with the <I>start/stop</I> keywords of
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the <A HREF = "run.html">run</A> command.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>The fix must be the first fix specified for a given run. The
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force/neigh <I>mode</I> should not be used with a triclinic box or
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<A HREF = "pair_hybrid.html">hybrid</A> pair styles.
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</P>
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<P>The <I>split</I> setting must be positive when using
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<A HREF = "pair_hybrid.html">hybrid</A> pair styles.
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</P>
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<P>Currently, group-ID must be all.
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</P>
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<P><B>Related commands:</B> none
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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