snap_release_v108.txt

SNAP Version 1.08
10/24/2018

SNAP Version 1.08 includes major revisions to the previous version of SNAP
released to GitHub. The new version has been rewritten to incorporate
similar changes mad to the code for which it is a proxy, PARTISN.

Summary:
SNAP 1.08 includes two major modifications. The major revisions are (1) the
implementation of a new thread-locking scheme when thread_multiple is not
available that is conformal with OpenMP standard in that any lock is set and
unset by the same thread before being used by any other thread; and (2) the
implementation of an asynchronous communication scheme that allows for
simultaneous mesh sweeps in multiple octant directions.

The thread-locking scheme required the relocation of the nested parallel OpenMP
region into the mkba_sweep subroutine. This means more fork/join operations and
will diminish performance. In the absence of nested threading, the new scheme
can lead to some small performance decrease as thread barriers are put in place
to protect against race conditions. The use of mkba_sweep is preserved for
research interest, so its performance has not been optimized.

The simultaneous octant sweeps algorithm improves parallel efficiency by
starting sweeps from multiple corners of fully known boundary conditions (two
in 2-D and four in 3-D; this restriction is meant to mimic the production code
which permits more restrictive boundary conditions, not just vacuum). The
algorithm works with threads for thread_serialized and thread_multiple
environments, but only a single lock is used with the former, because the
order does not matter. This algorithm offers improved scaling, increasingly
noticeable at increasing node-count. It represents the future direction for the
production code and as such has been made the default. It does not work with
swp_typ=1.

Please note some of the variable names and keywords previously used as
placeholders for the simultaneous octant sweeps algorithm have been changed
or removed. Most notably, cor_swp has been moved to multiswp as the input
keyword.

Minor changes were made to the Makefile for better GFORTRAN compile options and
remove some options for Intel KNL (ksnap) builds.

Please direct questions to the SNAP developers for finer details of the code
changes.


Modified files:
Makefile
control.f90
dim1_sweep.f90
dim3_sweep.f90
inner.f90
input.f90
mkba_sweep.f90
octsweep.f90
plib.F90
setup.f90
solvar.f90
sweep.f90
thrd_comm.f90
translv.f90
version.f