forked from lijiext/lammps
108 lines
4.1 KiB
HTML
108 lines
4.1 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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<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><I>mode</I> specifies where neighbor list calculations will be performed.
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If <I>mode</I> is force, neighbor list calculation is performed on the
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CPU. If <I>mode</I> is force/neigh, neighbor list calculation is
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performed on the GPU. GPU neighbor
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list calculation currently cannot be used with a triclinic box.
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GPU neighbor lists are not compatible with styles that are not GPU-enabled.
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When a non-GPU enabled style requires a neighbor list, it will also be
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built using CPU routines. In these cases, it will typically be more efficient
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to only use CPU neighbor list builds. For <A HREF = "pair_hybrid.html">hybrid</A> pair
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styles, GPU calculated neighbor lists might be less efficient because
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no particles will be skipped in a given neighbor list.
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</P>
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<P><I>first</I> and <I>last</I> specify the GPUs that will be used for simulation.
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On each node, the GPU IDs in the inclusive range from <I>first</I> to <I>last</I> will
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be used.
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</P>
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<P><I>split</I> can be used for load balancing force calculation work between
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CPU and GPU cores in GPU-enabled pair styles. If 0<<I>split</I><1.0,
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a fixed fraction of particles is offloaded to the GPU while force calculation
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for the other particles occurs simulataneously on the CPU. If <I>split</I><0,
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the optimal fraction (based on CPU and GPU timings) is calculated
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every 25 timesteps. If <I>split</I>=1.0, all force calculations for
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GPU accelerated pair styles are performed
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on the GPU. In this case, <A HREF = "pair_hybrid.html">hybrid</A>,
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<A HREF = "bond_style.html">bond</A>, <A HREF = "angle_style.html">angle</A>,
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<A HREF = "dihedral_style.html">dihedral</A>, <A HREF = "improper_style.html">improper</A>,
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and <A HREF = "kspace_style.html">long-range</A> calculations can be performed on the CPU
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while the GPU is performing force calculations for the GPU-enabled pair
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style.
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</P>
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<P>In order to use GPU acceleration, a GPU enabled style must be
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selected in the input script in addition to this fix. Currently,
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this is limited to a few <A HREF = "pair_style.html">pair styles</A>.
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</P>
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<P>More details about these settings and various possible hardware
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configuration are in <A HREF = "Section_start.html#2_8">this section</A> of the
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manual.
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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>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 force/neigh
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<I>mode</I> should not be used with a triclinic box or GPU-enabled pair styles
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that need <A HREF = "special_bonds.html">special_bonds</A> settings.
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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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