[petsc-users] strong-scaling vs weak-scaling

[Jed Brown]

Mark Adams <mfadams at lbl.gov> writes:
> I would guess it is the latter. 

In this case, definitely.

> It is hard to get "rollover" to the right.  You could get it on KNL
> (cache configuration of HBM) when you spill out of HBM.

Yes, but the same occurs if you start repeatedly spilling from some
level of cache, which can happen even if the overall data structure is
much larger than cache.  Not all algorithms have the flexibility to
choose tile sizes independently from problem size and specification;
it's easy to forget that this luxury is not universal when focusing on
dense linear algebra, for example.

> Personally, if you are you going to go into this much detail (eg, more than
> just one plot) I would show a plot of iteration count vs problem size, and
> be done with it, and then fix the iteration count for the weak scaling and
> dynamic range plot (I agree we could use a better name).

Alternatively, plot the performance spectrum (dynamic range) for the
end-to-end solve and per iteration.  The end user ultimately doesn't
care about the cost per iteration (and it's meaningless when comparing
to an algorithm that converges differently), so I'd prefer that the
spectrum for the end-to-end application always be shown.
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