Changes between Version 8 and Version 9 of doc/app/machine/hlrnIII

Timestamp:

Jan 13, 2015 3:32:48 PM (10 years ago)

Author:

raasch

Comment:

--

doc/app/machine/hlrnIII

@@ -1 +1 @@
 = Hints for using the Cray-XC30 at HLRN =
 
+* Performance issues with runs using larger number of cores
 * Running remote jobs 
 * Fortran issues
@@ -7 +8 @@
 \\
 
+
+== Performance issues with runs using larger number of cores ==
+
+Runs using the FFT pressure solver with core numbers > 10.000 may show substantially improved performance in case of setting the MPI environment variable {{{MPICH_GNI_MAX_EAGER_MSG_SIZE=16384}}} (the default value on the XC30 is 8192). It changes the threshold value for switching the data transfer with {{{MPI_ALLTOALL}}} from rendezvous to eager protocol.
+
+Setting can be realized by including an additional line in the configuration file, e.g.:
+{{{
+%IC:[[ \$localhost = lccrayb ]]  &&  export MPICH_GNI_MAX_EAGER_MSG_SIZE=16384
+}}}
 
 == Running remote jobs ==