[Trilinos-Users] Performance Question about Epetra_FECrsMatrix (and probably Tpetra::CrsMatrix too)

[Williams, Alan B]

Pat,
I haven't done any recent profiling of the FECrsMatrix fill operations. How high are the LID operations in your profile, compared to the fill in general and your coefficient-calculation code, etc.?

I believe the same issue occurs in Tpetra, since the matrix has to decide whether each contribution belongs on the local processor or not.

Perhaps a significant change is necessary to address this. One possibility would be to have the matrix not check local-vs-global for each row but instead store all contributions locally and only distinguish between local and non-local at the global-assemble step.

Alan


> -----Original Message-----
> From: trilinos-users-bounces at software.sandia.gov [mailto:trilinos-
> users-bounces at software.sandia.gov] On Behalf Of Pat Notz
> Sent: Wednesday, March 30, 2011 12:26 PM
> To: trilinos-users at software.sandia.gov
> Subject: [Trilinos-Users] Performance Question about Epetra_FECrsMatrix
> (and probably Tpetra::CrsMatrix too)
> 
> I'm doing typical FEM assemblies using an Epetra_FECrsMatrix and it
> appears to be working correctly. However, I've been profiling the
> serial performance and I have some concerns.
> 
> In general, we're making off-processor contributions so we have to use
> global row/col ids. The SumIntoGlobalValues method does some
> gymnastics to see if the contributions are local or global and that
> results in a lot of calls to LID(gid) -- it's LID() that's showing up
> high in my profile.
> 
> As far as I can tell, it appears that you can use local ids for
> locally *owned* contributions but there's no notion of an equally
> cheap local id for shared-but-not-owned contributions. Is that right?
> 
> I'm open to switching to Tpetra if things are better there (I may be
> switching anyway).
> 
> ~ Pat
> 
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