[Trilinos-Users] Cache performance of Trilinos MatVec

[James C. Sutherland]

Mike et al,

I have tried building trilinos with OSKI.  It appears that the OSKI  
examples are not built (at least in 9.0.2 which I am using).  Do you  
have local builds or regression tests that are functional with OSKI?   
Is there a way of building the examples through the trilinos build  
system?

I am having runtime errors when trying to use OSKI matrices rather  
than CRS matrices in my application.  I am trying to discern whether  
this is a problem in my usage of Epetra_OskiMatrix or if there is a  
problem in the trilinos interface to OSKI.

FYI, it looks like the new CMake build system is even less aware of  
OSKI.

James
---
James C. Sutherland
Assistant Professor, Chemical Engineering
The University of Utah
50 S. Central Campus Dr, 3290 MEB
Salt Lake City, UT 84112-9203
(801) 585-1246
http://www.che.utah.edu/~sutherland

On Jun 10, 2009, at 8:16 AM, Heroux, Michael A wrote:

> James,
>
> As Alan mentioned, sparse MV is notorious for poor cache  
> performance.  Some of the best work in addressing this issue has  
> been done by the BeBOP project at UC-Berkeley in the OSKI library.   
> Epetra can use OSKI for sparse operations via Epetra_Oski* classes.   
> These classes rely on the OSKI library (which you download and build  
> yourself).  The following tech report describes the interface and  
> performance results:
>
> http://trilinos.sandia.gov/packages/epetra/IanKarlin.pdf
>
> You might also consider the Epetra_JadMatrix class, which can work  
> well on the latest microprocessors that support streaming well.   
> Epetra_JadMatrix can be especially useful for very sparse matrices  
> (the 3-4 nonzeros per row collections you have).  It is a just a few  
> line change to your code to try these options.
>
> Mike
>
>
> On 6/10/09 9:01 AM, "Alan Williams" <william at sandia.gov> wrote:
>
>
>
> James,
> For matrix-vector product y = A*x, the core of the sparse matvec is  
> a statement like this:
>   y[i] += Acoefs[j]*x[Acols[j]]
>
> So depending on how the column-indices of A are ordered, lots of  
> cache misses in the x vector could occur.
> A matrix reordering may help in some cases.
>
> Alan
>
>
> > -----Original Message-----
> > From: trilinos-users-bounces at software.sandia.gov
> > [mailto:trilinos-users-bounces at software.sandia.gov] On Behalf
> > Of James C. Sutherland
> > Sent: Tuesday, June 09, 2009 5:23 PM
> > To: trilinos-users at software.sandia.gov
> > Subject: [Trilinos-Users] Cache performance of Trilinos MatVec
> >
> > Does anyone know if there has been a study of, or effort to
> > optimize,
> > cache performance of MatVec operations in Trilinos?
> >
> > Specifically, I am finding that epetra_dcrsmv (sparse matvec) has
> > extremely bad cache performance (lots of cache misses) on an intel
> > chipset that I have.  This seems to be problematic for a range of
> > matrix sizes.  I have very sparse matrices (3-10 nonzero entries per
> > row), and these can range in size from O(10^2-10^10^5) rows.
> >
> > Any thoughts?
> >
> > James
> >
> > _______________________________________________
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> > Trilinos-Users at software.sandia.gov
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> >
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