README.bgl

This summarises some info for the Blue Gene light system

The configure command should be something like the following:

path-to-the-sources/configure --host=ppc-ibm-blrts --build=ppc64-ibm-linux \
--without-lapack --enable-mpi --with-mpidimension=4 \
--enable-gaugecopy --with-limedir=path-to-lime/  \
--enable-newdiracop CC=/usr/bin/blrts_xlc CPPFLAGS=-I/bgl/BlueLight/ppcfloor/bglsys/include/ \
--with-nonblockingmpi --with-persistentmpi --with-bgldram

some comments are important: 
- if option --with-bgldram is used, then the executables have to be
  relinked with /bgl/local/bin/blrts_gcc -Xlinker --script=./elf32ppcblrts.x .
  The linker is now replaced automatically.
  the file elf32ppcblrts.x can be obtained from
  blrts-gnu/powerpc-bgl-blrts-gnu/lib/ldscripts/elf32ppcblrts.x
  and it needs the change of the line
  PROVIDE (__executable_start = 0x00200000); . = 0x00200000 + SIZEF_HEADERS;
  to
  PROVIDE (__executable_start = 0x01000000); . = 0x01000000 + SIZEF_HEADERS;

  otherwise the code will stop with the message that there is not enough memory
  for halfspinor fields. 

  note that this option is default for the BGL build!

- the new Dirac operator implementation is useful for bad boundary to volume
  ratios. In case of large local volumes it might be better to use 
  --disable-newdiraop

- running should be done with something like 
  -env "BGLMPI_EAGER=500000000 BGLMPI_PACING=n"
  as options to mpirun.