[OMPI users] built-in memchecker support

[Dave Love]

Apropos configuration parameters for packaging:

Is there a significant benefit to configuring built-in memchecker
support, rather than using the valgrind preload library? I doubt being
able to use another PMPI tool directly at the same time counts.

Also, are there measurements of the performance impact of configuring,
but not using, it with recent hardware and software? I don't know how
relevant the results in https://www.open-mpi.org/papers/parco-2007/
would be now, especially on a low-latency network.

[Christoph Niethammer]

Hi Dave,

The memchecker interface is an addition which allows other tools to be used as well.

A more recent one is memPin [1].
As stated in the cited paper, the overhead is minimal when not attached to a tool.
From my experience a program running under pin tool control runs much faster than valgrind.

Best
Christoph Niethammer

[1] http://www.springer.com/cda/content/document/cda_downloaddocument/9783642373480-c1.pdf?SGWID=0-0-45-1397615-p175067491



----- Original Message -----
From: "Dave Love" <***@manchester.ac.uk>
To: "Open MPI Users" <***@lists.open-mpi.org>
Sent: Thursday, August 24, 2017 1:22:17 PM
Subject: [OMPI users] built-in memchecker support

Apropos configuration parameters for packaging:

Is there a significant benefit to configuring built-in memchecker
support, rather than using the valgrind preload library? I doubt being
able to use another PMPI tool directly at the same time counts.

Also, are there measurements of the performance impact of configuring,
but not using, it with recent hardware and software? I don't know how
relevant the results in https://www.open-mpi.org/papers/parco-2007/
would be now, especially on a low-latency network.

[Gilles Gouaillardet]

Dave,

the builtin memchecker can detect MPI usage errors such as modifying
the buffer passed to MPI_Isend() before the request completes

all the extra work is protected
if ( running_under_valgrind() ) {
extra_checks();
}

so if you are not running under valgrind, the overhead should be unnoticeable

Cheers,

Gilles

On Thu, Aug 24, 2017 at 8:37 PM, Christoph Niethammer

Post by Christoph Niethammer
Hi Dave,
The memchecker interface is an addition which allows other tools to be used as well.
A more recent one is memPin [1].
As stated in the cited paper, the overhead is minimal when not attached to a tool.
From my experience a program running under pin tool control runs much faster than valgrind.
Best
Christoph Niethammer
[1] http://www.springer.com/cda/content/document/cda_downloaddocument/9783642373480-c1.pdf?SGWID=0-0-45-1397615-p175067491
----- Original Message -----
Sent: Thursday, August 24, 2017 1:22:17 PM
Subject: [OMPI users] built-in memchecker support
Is there a significant benefit to configuring built-in memchecker
support, rather than using the valgrind preload library? I doubt being
able to use another PMPI tool directly at the same time counts.
Also, are there measurements of the performance impact of configuring,
but not using, it with recent hardware and software? I don't know how
relevant the results in https://www.open-mpi.org/papers/parco-2007/
would be now, especially on a low-latency network.
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[Dave Love]

Post by Gilles Gouaillardet
Dave,
the builtin memchecker can detect MPI usage errors such as modifying
the buffer passed to MPI_Isend() before the request completes

OK, thanks. The implementation looks rather different, and it's not
clear without checking the code in detail how it differs from the
preload library (which does claim to check at least some correctness) or
why that that sort of check has to be built in.

Post by Gilles Gouaillardet
all the extra work is protected
if ( running_under_valgrind() ) {
extra_checks();
}
so if you are not running under valgrind, the overhead should be unnoticeable

Thanks. Is there a good reason not to enable it by default, then?
(Apologies that I've just found and checked the FAQ entry, and it does
actually say that, in contradiction to the paper it references. I
assume the implementation has changed since then.)

A deficiency of the preload library I just realized is that it says it's
only MPI-2.

[Dave Love]

Post by Christoph Niethammer
Hi Dave,
The memchecker interface is an addition which allows other tools to be used as well.

Do you mean it allows other things to be hooked in other than through
PMPI?

Post by Christoph Niethammer
A more recent one is memPin [1].

Thanks, but Pin is proprietary, so it's no use as an alternative in this
case.