[PVFS-users] terrible performance ... help!

[Robert Latham]

On Mon, May 23, 2005 at 06:21:19PM -0400, Kaveh Moallemi wrote:
> My question is, with the current setup, why does the non-pvfs version
> of my program performe so much better (fprintf() vs. pvfs_write())?
> Note that both versions work out of the same pvfs mounted directory.

fprintf() (and the other <stdio.h> routines) make use of caches and
buffers.  pvfs_write() does no caching and is more analagous to
unix write().  Each call to pvfs_write means you will go over the
network to the io servers.  

It's quite likely that calls to fprintf will end up getting buffered
and serviced in one network round trip. 

I don't know how familiar you are with MPI-IO, but you might want to
look into the MPI_File_* routines, particularly the support for
collective and noncontigous IO.

==rob

-- 
Rob Latham
Mathematics and Computer Science Division    A215 0178 EA2D B059 8CDF
Argonne National Labs, IL USA                B29D F333 664A 4280 315B