[petsc-dev] Seeming performance regression with GAMG

[Lawrence Mitchell]

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On 27/04/15 16:06, Lawrence Mitchell wrote:
> Dear all,
> 
> we recently noticed a slowdown when using GAMG that I'm trying to
> track down in a little more detail.  I'm solving an Hdiv-L2
> "helmholtz" pressure correction using a schur complement.  I
> precondition the schur complement with 'selfp', which morally looks
> like a normal Helmholtz operator (except in the DG space).  The domain
> is very anisotropic (a thin atmospheric shell), so getting round to
> trying Toby's column-based coarsening plugin is on the horizon but I
> haven't done it yet.
> 
> I don't have a good feel for exactly when things go worse, but here
> are two data points:
> 
> A recentish master (e4b003c), and master from 26th Feb (30ab49e4).  I
> notice in the former that MatPtAP takes significantly longer (full
> logs below), different coarsening maybe?  As a point of comparison,
> the PCSetup for Hypre takes ballpark half a second on the same operator.
> 
> I test with KSP ex6 (with a constant RHS):
> 
> Any ideas?

I should have mentioned, a MatLoadable matrix is available at:

http://www.doc.ic.ac.uk/~lmitche1/

Lawrence

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