[cig-commits] r19519 - seismo/3D/SPECFEM3D_GLOBE/trunk/doc/USER_MANUAL

[dkomati1 at geodynamics.org]

Author: dkomati1
Date: 2012-01-30 14:12:56 -0800 (Mon, 30 Jan 2012)
New Revision: 19519

Modified:
   seismo/3D/SPECFEM3D_GLOBE/trunk/doc/USER_MANUAL/manual_SPECFEM3D_GLOBE.pdf
   seismo/3D/SPECFEM3D_GLOBE/trunk/doc/USER_MANUAL/manual_SPECFEM3D_GLOBE.tex
Log:
added more details about _HANDOPT


Modified: seismo/3D/SPECFEM3D_GLOBE/trunk/doc/USER_MANUAL/manual_SPECFEM3D_GLOBE.pdf
===================================================================
(Binary files differ)

Modified: seismo/3D/SPECFEM3D_GLOBE/trunk/doc/USER_MANUAL/manual_SPECFEM3D_GLOBE.tex
===================================================================
--- seismo/3D/SPECFEM3D_GLOBE/trunk/doc/USER_MANUAL/manual_SPECFEM3D_GLOBE.tex	2012-01-30 22:06:33 UTC (rev 19518)
+++ seismo/3D/SPECFEM3D_GLOBE/trunk/doc/USER_MANUAL/manual_SPECFEM3D_GLOBE.tex	2012-01-30 22:12:56 UTC (rev 19519)
@@ -274,8 +274,13 @@
 
 Some do-loops have been modified using a common technique to help compilers enhance pipelining and make better use
 of the cache. If you want to use these hand-optimized loops, add an additional flag ``\texttt{-D\_HANDOPT}'' to your compiler options
-(with the IBM xlf compiler, change this to ``\texttt{-WF,-D\_HANDOPT}''). Use this option only if you know what you are doing, i.e., compare the seismograms
-obtained with and without this option on your machine and make sure they are all identical down to roundoff noise.\\
+(with the IBM xlf compiler, change this to ``\texttt{-WF,-D\_HANDOPT}'').
+BEWARE: we have observed that using \_HANDOPT in combination with -O3 or higher can lead to problems on some machines;
+Thus, use this option only if you know what you are doing.
+At the very least, run the same test simulation once with \_HANDOPT and once without
+and make sure that all the seismograms you get (after convolution with a source time function, otherwise the raw seismograms before
+convolution are too sensitive to roundoff noise) are the same down to roundoff noise.
+You can do this for instance with the example given in EXAMPLES/small\_benchmark\_run\_to\_test\_a\_new\_machine.
 
 If you run very large meshes on a relatively small number
 of processors, the memory size needed on each processor might become