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

[Troy Baer]

On Mon, 2005-05-23 at 16:52 -0400, Kaveh Moallemi wrote:
> I'm getting terrible performance using pvfs calls ... far worst than
> using regular (non-pvfs) IO.  I've provided a code snip below ... does
> anyone see something wrong with it?
> 
> I'm using PVFS version 1.6.2 with a single iod (for the time being). 
> I've noticed that with the non-pvfs version of my program, the iod
> runs at about 10% CPU.  And, with the pvfs version, the iod runs in
> excess of 80% CPU time!

PVFS with a single iod and a single client is not likely to perform
well; the whole point of the file system's design is to to have multiple
servers and multiple clients to increase the amount of aggregate
bandwidth available.  In addition, it's not clear from the code snippet
you posted what the size of pvfs_buffer is, but if it's less than 64kB
(the default stripe size for a file on PVFS), you're even less likely to
see good performance.

What are you trying to accomplish here?  PVFS is *not* a general purpose
file system, so it does some things (eg. parallel I/Os to/from multiple
hosts with very large block sizes) very well and others (eg. I/O to/from
a single host with very small block sizes) rather badly.

	--Troy
-- 
Troy Baer                       troy at osc.edu
Science & Technology Support    http://www.osc.edu/hpc/
Ohio Supercomputer Center       614-292-9701