[Dune] [#506] Coarsening of ALUGrid very slow on large grids

[Dune]

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User who did this - Uli Sack (usack) 

Attached to Project - Dune
Summary - Coarsening of ALUGrid very slow on large grids
Task Type - Bug Report
Category - Grid
Status - Unconfirmed
Assigned To - 
Operating System - Linux
Severity - Medium
Priority - Normal
Reported Version - SVN
Due in Version - Undecided
Due Date - Undecided
Details - Hi Dune!

I have had an ALUGrid (sequential) of roughly 18mio nodes that was coarsened in two successive marking and adapting cycles to about 4.8mio nodes. This took about 14 hours (!!!) on a 64Bit SuSe10 system running on a machine with 256GB RAM (and 8...)
model name      : Dual-Core AMD Opteron(tm) Processor 8220
cpu MHz         : 2792.922
cache size      : 1024 KB
Same thing for about 9mio to 2.5mio nodes took round about 3,5h, 4.9mio->1.3mio 24min. This has a somewhat quadratic feel.
Adding some stopwatches showed that more than 95% of that time goes into the preAdapt(),adapt(),postAdapt() cycle. I guess it actually goes into the adapth() method but I'm checking on that right now.

Would you happen to know where the implementation of the coarsening might cause quadratic (or let's say nonlinear) runtime?

tnx,
Uli


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