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<p class=MsoNormal>Hi FLASH users,<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I’m currently running FLASH at the New York Blue
BlueGene/L and P machines. I ran into a couple of issues that users of
the BlueGene machines should be aware of. The first issue is more of a
question…<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Being relatively new to FLASH, I was using Makefile.h files
from other sites directories for BlueGene machines to base my own Makefile off
of. In addition, I was also reading the man pages for IBM’s XL
compilers. I found an inconsistency with one of the compiler options. In
most of the sites directories using BlueGene machines, the compiler option
qcache is set as -qcache=auto. However, reading through the man pages of blrts_xlf90,
I found that the -qcache option’s default changes depending on what is
set by the qarch option. Furthermore, according to the man pages,
-qcache=auto optimizes the cache for the compiling machine, i.e. the
login-node, not the compute-nodes. Is there any reason not to trust the
man pages?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Also, while I’m discussing XL compilers, what other
compiler options have other “FLASH on BlueGene” users found useful
/ successful at optimization? I’m currently only able to utilize
-O2 optimization.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The second issue, which is more of a notice/warning, is that
I’ve been trying to track down a bug in my code used within FLASH.
I was putting the result of a linear interpolation into a power, i.e.
10.0**<result>. I was getting inconsistent results on BG/L even
with the same executable. It turns out that making 10.0 into 10.0e0 fixes
this. I subsequently found a compiler option which promotes all real
constants to double precision for the XL compilers, -qdpc=e. I suggest
using this along with setting the real default to be 8 bytes.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Aaron Jackson<o:p></o:p></p>
<p class=MsoNormal>Department of Physics & Astronomy<o:p></o:p></p>
<p class=MsoNormal>Stony Brook University<o:p></o:p></p>
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