Cray and PETSc

[Stephen R Ball]

Hi Adrian

You know me already, as I have already accepted to be a tester for your
Cray optimised version of PETSc. I just thought that I would chip in
here and let you know what external packages we currently use with
PETSc. These are Hypre, Spooles and ML.

Regards

Stephen R. Ball
Parallel Technology Support
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e-mail: stephen.r.ball at awe.co.uk



-----Original Message-----
From: owner-petsc-dev at mcs.anl.gov [mailto:owner-petsc-dev at mcs.anl.gov]
On Behalf Of Adrian Tate
Sent: 23 August 2007 19:22
To: Tom Cortese
Cc: Barry Smith; petsc-developers at mcs.anl.gov; petsc-dev at mcs.anl.gov;
Keita Teranishi
Subject: EXTERNAL: RE: Cray and PETSc

Tom 

Thanks for your comments - I'm sure your experiences with PETSc on Crays
will be helpful to us. Perhaps Keita and I could communicate directly
with you on these issues and to find out more about the requirements of
your users?

It is our ultimate goal to provide everything that Cray customers need
with PETSc, but I can't comment on how feasible that is without knowing
more about the packages that are widely used. For our initial release we
were thinking of providing HYPRE and ParMETIS, we also provide SuperLU
already within Cray LibSci. MUMPS is certainly something we should
consider. 

This is a perfect opportunity to ask PETSc developers that use Cray
hardware to suggest packages that they'd like to see provided by Cray. 

Adrian

-----Original Message-----
From: Tom Cortese [mailto:tcortese at cs.utk.edu] 
Sent: Thursday, August 23, 2007 10:53 AM
To: Adrian Tate
Cc: Barry Smith; petsc-developers at mcs.anl.gov; petsc-dev at mcs.anl.gov;
Keita Teranishi
Subject: RE: Cray and PETSc

Hello all,

First of all, I am NOT a PETSc developer, but as a member of the DoD HPC

Modernization Program I DO install PETSc on a wide variety of hardware 
platforms (including XT3, XD1, and even X1 [that was rough; had to 
cross-compile on one machine and transfer files]), and have had numerous

email exchanges working out all of the little quirks involved in 
installing PETSc on these machines, so the PETSc folks have been kind 
enough to let me watch this development email list.

I hope I'm not over-stepping my bounds by asking this, but I have two 
comments:

1)  Making PETSc available on the Cray machines sounds like a GREAT idea

2)  Several of our users also like to have packages such as HYPRE and 
MUMPS, etc... installed along with PETSc.  Would such external packages 
also be installed by Cray, or would users requiring a combination of,
say, 
PETSc and MUMPS still have to make their own installation?

Thanks,

 	-Tom Cortese
 	PET Computational Environnment Onsite

On Thu, 23 Aug 2007, Adrian Tate wrote:

>
> Hi Barry
>
> Thanks for your reply.
>
> We will expect to provide the new full releases of PETSc as soon as we
possibly can. Obviously there is something of a lag because Cray need to
test, package and release the library, but we'll try to do so with
minimal delay. Obviously any heads-up you can give us in advance will
help reduce the lag. With respect to patch versions, it is going to be
very difficult for Cray to release every new version, and by looking at
the logs it seems that many of the patches would not be relevant to a
Cray specific build. We will endeavor to monitor all patch releases and
will go with an unscheduled new release of PETSc when we see a relevant
patch. One thing that we can do to minimize confusion is to informally
provide the most currently patched version to any customer who is
experiencing a problem, although we might not go with a full release of
the version in question.
>
> Regarding Cray modifications, we (Keita Teranishi or myself) will
check in periodically with you to show you our improvements and to see
which, if any need to be channeled back into the PETSc build.
>
> I hope this support structure works OK from your perspective and I
look forward to working with the PETSc team.
>
> Thanks!
> Adrian
>
> -----Original Message-----
> From: Barry Smith [mailto:bsmith at mcs.anl.gov]
> Sent: Monday, August 20, 2007 11:12 AM
> To: Adrian Tate
> Cc: petsc-developers at mcs.anl.gov; petsc-dev at mcs.anl.gov
> Subject: Re: Cray and PETSc
>
>
>   Adrian,
>
>    Thank you for in the inquiry.
>
>
> On Thu, 16 Aug 2007, Adrian Tate wrote:
>
>> Hello Barry
>>
>> I'm not sure we met in person - I am the lead of the libraries group
>> at Cray. We decided some time ago that our iterative solver strategy
>> would be to leverage PETSc, and to hopefully provide some Cray
>> specific tunings to improve performance of the KSP solvers (largely
>> through our custom sparse BLAS and some parallel tuning for our
>> interconnect). I believe that John Lewis has been in communication
>> with you with respect to the tuning of Sparse BLAS and their
>> integration with the PETSc build.
>>
>> We are however, considering packaging and supplying PETSc along with
>> the scientific library that we provide (libSci). This allows for
>> better integration of our internal kernels and also it means that we
>> are no longer requiring users (including benchmakers and internal
>> users) to build their own PETSc. I see from your online page that
>> doing so is acceptable as long as we use a copyright switch during
>> configure. By applying this switch, do we make our PETSc library
>> unsupported from your perspective?
>
>   The GNU copyright code is tiny; it would not effect the usability
> or support of PETSc
>
>> We do not expect to be able to
>> provide anywhere near the degree of support that your team provide,
>> and I was hoping to supply a pre-built library whose users could
still
>> seek assistance through your normal support channels - is this
>> realistic?
>>
>   Yes.
>
>   The two isses that concern us with pre-packaged versions of PETSc
are
> 1) keeping up to date on our releases. We generally make two releases
> a year and much prefer that users use the most recently release.
> If they are using an older release it means we are less able to help
> them.
> 2) keeping up to date on our patches. We may make several bug patches
> to each release. Users with a pre-packaged version have trouble
keeping
> up with the source code patches we provide.
>
>>
>>
>>
>>
>> Also, I would be interested to know your degree of interest in the
>> Cray-specific modifications that we make - would you prefer those to
>> be channeled back into the PETSc library?
>
>  If they involved directly changing PETSc code, we much prefer to get
> it channeled back into the master copy of the source code. Makes it
> much easier to debug user code. If it is auxiliary code, like a faster
> ddot() etc then it is more appropriate to not try to include it.
>
>> Any other comments you have
>> on the way that Cray can contribute to the PETSc project, I would be
>> very glad to hear.
>
>  PETSc has a variety of "tuning factors" that could theoretically be
> set optimally for a particular machine, these range from simple things
> like compiler options, to a choice between C and Fortran versions of
> the same code (what we call them Fortran kernels), to different loop
> unrollings (in the inline.h file), even something like PetscMemzero()
> which has five possible forms. Now currently we do not tune these
> or even have a test harness for selecting a good tuning. One thing
> you could/would like to do, is determine good choices for these
> options on your machines. Just as a simple example, on some Linux
systems
> the basic libraries are just compiled with the GNU compiler, hence the
> system memset() is not particularly effective. A version compiled of
PETSc
> compiled using a "Fortran memset" may be much faster, or Intel
provides
> its own _intel_fast_memset() which is better. I've seen a few percent
> increase in performance of entire nonlinear PDE solver applications
> just from using the non-default memset(). [This was specifically on
> an Itanium system, but is likely on other configurations also].
>
>
>   Barry
>
>
>>
>>
>>
>> Regards,
>>
>>
>> Adrian Tate
>>
>> ---
>>
>> Technical Lead
>>
>> Math Software
>> Cray Inc.
>>
>> (206) 349 5868
>>
>>
>
>
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