[svn-r11950] Purpose:

Enhanced collective chunk IO supports

Description:
1. When using collective IO with chunking storage without any tuning, performance may become worse under some circumstances.
2. Current HDF5 handles raw-data IO per chunk. So for many small chunks, many small IOs will be passed into MPI-IO. That may cause bad performance.
3. For one IO per chunk case, sometimes performance with collective is worse than performance with independent. An obvious case is when only one process is doing IO and all other process are not doing IO, the collective IO will only add overheads for communication. We want to avoid this case. Some management inside our library needs to be done.


Solution:
- Added managements of collective IO supports for chunking storage
         inside parallel HDF5
         1) Implemented One IO with collective mode for all chunks in the
            application by building one MPI derived datatype accross all
            chunks.
         2) Implemented the decision-making support to do collective IO inside
            MPI-IO per chunk.
         3) Added the decision-making support to do one IO accross all chunks
            or to do multiple IOs with each IO per chunk.
         4) Added the support to handle the case some processes won't do any IOs in
            collectively.
         5) Some MPI-IO package(mpich 1.2.6 or lower, e.g.) cannot handle
            collective IO correctly for the case when some processes have no
            contributions to IOs, a special macro is added to change
            collective IO mode to independent IO mode inside HDF5 library.



Platforms tested:

Parallel:

IBM AIX 5.2(copper)
Linux (heping) mpich-1.2.6
SDSC Teragrid mpich-1.2.5
Linux(Tungsten) mpich-1.2.6
Altix(NCSA cobalt)

Seq:
Linux(heping)

Misc. update:

0 files changed, 0 insertions, 0 deletions