[Darshan-users] no write information when using mvapich2

Rob Latham robl at mcs.anl.gov
Fri Jul 26 08:04:15 CDT 2013

On Thu, Jul 25, 2013 at 11:19:20PM -0400, Phil Carns wrote:
> Just a quick follow up for mailing list archival purposes.  We
> discussed this problem a little bit more off-list and it looks like
> the issue is related to tracking AIO operations issued by the
> nonblocking I/O functions in MPI-IO. Here is a trac ticket with some
> more information:
>     http://trac.mcs.anl.gov/projects/darshan/ticket/115
> I don't know why this is being triggered in mvapich but not openmpi
> in David's case, but I'm able to reproduce it with a recent mpich
> build as well.  We'll continue to look into it further.

I bet it's because OpenMPI does not support "extended generalized
requests", which means ROMIO will deal with non-blocking requests by
just doing all the I/O up front.


> thanks,
> -Phil
> On 07/19/2013 01:06 PM, David Shrader wrote:
> >Hello All,
> >
> >I am currently trying to bring up a Darshan build that supports
> >mvapich2 1.7 and 1.8. The build seemingly completes without an
> >issue, but I have noticed a problem when running an IO-replication
> >application that we like to use: I am getting no stats in terms of
> >writes. The app's general flow is to do a writing phase and then a
> >reading phase to a single file (no collective operations except
> >when opening the file). The stats for the reading phase are about
> >what I expect. However, the stats for the writes are all 0.
> >Specifically, CP_BYTES_WRITTEN and CP_POSIX_WRITES are both 0. The
> >corresponding READS counters are where they should be.
> >
> >I have tested this app (with the same run command) using a build
> >of Darshan that works with Open MPI. There, the WRITE-related
> >counters I mentioned above are where I expect them to be. It is
> >just the mvapich2 builds that have this behavior.
> >
> >Did I miss something when building for mvapich2? Any ideas as to
> >why write information might be missing? If it helps, I can send
> >some of the output from darshan-parser (there is only a single
> >file being written to, so the output isn't that large) or the log
> >file itself.
> >
> >Thanks,
> >David
> >
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Rob Latham
Mathematics and Computer Science Division
Argonne National Lab, IL USA

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