This is an email from 3 years ago... no one responded :-) This is coming up again because we're looking at "array variables" again... and this would be a large optimization.
Any comments? Derek On Wed, Aug 3, 2016 at 9:38 AM Derek Gaston <fried...@gmail.com> wrote: > I'm working on some low-level optimization stuff... and one of the things > I want to do is more vectorization when computing the value of variables > and when computing residuals, etc. I'm using the variable groups stuff to > be able to do large vector operations. > > To that end... I think that the current choice for dof-ordering within > variable groups could be changed to be more amenable to vectorization. > > Currently DofObject uses dof numbering based on this ordering for variable > groups: > > id = base + var_in_vg*ncomp + comp > > The problem with this is that I would like to do a vector operation that > is like this: > > phi_i * all_dofs_in_var_group_corresponding_to_i > > With any FE types that have more than one component the above ordering > means that the dofs corresponding to that shape function are spread out in > memory (i.e. they're NOT contiguous) and that would preclude vectorization > of the above operation. > > Instead, if we use a dof ordering like this: > > id = base + comp*n_var_in_vg + var_in_vg > > All of the dofs that need to multiply the same shape function would be > contiguous and easily vectorized. > > I don't think this change would effect anyone. We've never guaranteed > this ordering (and it's fairly new anyway)... I think everyone is probably > using the API instead of thinking of raw memory access like this (And I > know I probably should be too... but I've been doing it that way for over > 10 years and I have a few applications that have hundreds to > tens-of-thousands of variables now that could really use this optimization). > > What say you? > > Derek > >
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