[MPICH] FLASH IO over Jaguar

[Yu, Weikuan]

Hi, Rob,

> 
> Thanks Weikuan.  How did you determine these numbers?  I'll 
> add them to the benchmark. 

They were initially based on the numbers in the code for CHIBA. But I
used these numbers based on fairly extensive tests. 

-- HDF5 parameters. I checked on differences choice of HDF5 parameters,
there are not much differences. 
-- Collective buffer size. Default 4MB is too small. Increasing it to
16MB+ provided good performance improvement. Beyond 32MB, there is not
much gains.
-- Number of IO Aggregators. Perferred to be 512 or 1K. Too many of them
can be detrimental. This is not set in the patch because people may run
with nprocs < 1K. 

BTW, in terms of IO aggregators and collective buffer size, the same
seems to be true with NAS BT-IO over Cray XT.

--
Weikuan Yu
http://ft.ornl.gov/~wyu