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<div id="version" align=right><b>petsc-3.4.2 2013-07-02</b></div>
<A NAME="PetscHMPISpawn"><H1>PetscHMPISpawn</H1></A>
Initialize additional processes to be used as "worker" processes. This is not generally called by users. One should use -hmpi_spawn_size <n> to indicate that you wish to have n-1 new MPI processes spawned for each current process.
<H3><FONT COLOR="#CC3333">Synopsis</FONT></H3>
<PRE>
#include "petscsys.h"
PetscErrorCode PetscHMPISpawn(PetscMPIInt nodesize)
</PRE>
Not Collective (could make collective on MPI_COMM_WORLD, generate one huge comm and then split it up)
<P>
<H3><FONT COLOR="#CC3333">Input Parameter</FONT></H3>
<DT><B>nodesize </B> -size of each compute node that will share processors
<br>
<P>
<H3><FONT COLOR="#CC3333">Options Database</FONT></H3>
<DT><B>-hmpi_spawn_size nodesize</B> -
Notes: This is only supported on systems with an MPI 2 implementation that includes the MPI_Comm_Spawn() routine.
<br>
<P>
<pre>
Comparison of two approaches for HMPI usage (MPI started with N processes)
</pre>
<pre>
</pre>
<pre>
-hmpi_spawn_size <n> requires MPI 2, results in n*N total processes with N directly used by application code
</pre>
<pre>
and n-1 worker processes (used by PETSc) for each application node.
</pre>
<pre>
You MUST launch MPI so that only ONE MPI process is created for each hardware node.
</pre>
<pre>
</pre>
<pre>
-hmpi_merge_size <n> results in N total processes, N/n used by the application code and the rest worker processes
</pre>
<pre>
(used by PETSc)
</pre>
<pre>
You MUST launch MPI so that n MPI processes are created for each hardware node.
</pre>
<pre>
</pre>
<pre>
petscmpiexec -n 2 ./ex1 -hmpi_spawn_size 3 gives 2 application nodes (and 4 PETSc worker nodes)
</pre>
<pre>
petscmpiexec -n 6 ./ex1 -hmpi_merge_size 3 gives the SAME 2 application nodes and 4 PETSc worker nodes
</pre>
<pre>
This is what would use if each of the computers hardware nodes had 3 CPUs.
</pre>
<pre>
</pre>
<pre>
These are intended to be used in conjunction with USER HMPI code. The user will have 1 process per
</pre>
<pre>
computer (hardware) node (where the computer node has p cpus), the user's code will use threads to fully
</pre>
<pre>
utilize all the CPUs on the node. The PETSc code will have p processes to fully use the compute node for
</pre>
<pre>
PETSc calculations. The user THREADS and PETSc PROCESSES will NEVER run at the same time so the p CPUs
</pre>
<pre>
are always working on p task, never more than p.
</pre>
<pre>
</pre>
<pre>
See <A HREF="../PC/PCHMPI.html#PCHMPI">PCHMPI</A> for a PETSc preconditioner that can use this functionality
</pre>
<pre>
</pre>
<P>
For both <A HREF="../Sys/PetscHMPISpawn.html#PetscHMPISpawn">PetscHMPISpawn</A>() and <A HREF="../Sys/PetscHMPIMerge.html#PetscHMPIMerge">PetscHMPIMerge</A>() <A HREF="../Sys/PETSC_COMM_WORLD.html#PETSC_COMM_WORLD">PETSC_COMM_WORLD</A> consists of one process per "node", PETSC_COMM_LOCAL_WORLD
consists of all the processes in a "node."
<P>
In both cases the user's code is running ONLY on <A HREF="../Sys/PETSC_COMM_WORLD.html#PETSC_COMM_WORLD">PETSC_COMM_WORLD</A> (that was newly generated by running this command).
<P>
<P>
<P>
<H3><FONT COLOR="#CC3333">See Also</FONT></H3>
<A HREF="../Sys/PetscFinalize.html#PetscFinalize">PetscFinalize</A>(), PetscInitializeFortran(), <A HREF="../Sys/PetscGetArgs.html#PetscGetArgs">PetscGetArgs</A>(), <A HREF="../Sys/PetscHMPIFinalize.html#PetscHMPIFinalize">PetscHMPIFinalize</A>(), <A HREF="../Sys/PetscInitialize.html#PetscInitialize">PetscInitialize</A>(), <A HREF="../Sys/PetscHMPIMerge.html#PetscHMPIMerge">PetscHMPIMerge</A>(), <A HREF="../Sys/PetscHMPIRun.html#PetscHMPIRun">PetscHMPIRun</A>()
<BR>
<P>
<P><B><P><B><FONT COLOR="#CC3333">Level:</FONT></B>developer
<BR><FONT COLOR="#CC3333">Location:</FONT></B><A HREF="../../../src/sys/objects/mpinit.c.html#PetscHMPISpawn">src/sys/objects/mpinit.c</A>
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