Re: [Libmesh-devel] What's so slow with METHOD=dbg?

[Roy S. <roy...@ic...>]

On Tue, 6 Jun 2006, Kirk, Benjamin (JSC-EG) wrote:

> My guess is the
>
> #ifdef DEBUG
>  ...
> #endif
>
> Block in the dof_map.h header file at line 563.
>
> Try commenting that idfef out and see how it goes...

Did I ever get back to you on this?  I think I was in the middle of
writing a reply when something urgent came up.

Anyway, with that ifdef commented out, compute_sparsity_pattern is
about 320 times slower in dbg mode than in opt mode.  This is a
significant improvement over the original 350 times slower, but it's
still far short of the ~10 times slower I'd hoped for.

Don't worry about it, though.  The time I spend waiting for a slow
compute_sparsity_pattern() is still much less then the time you'd have
to spend figuring out how to optimize it... especially if the
optimization is impossible.  There's a lot of STL stuff in there and
in DEBUG mode the gcc STL turns on all sorts of slow bug checking
code.
---
Roy