[petsc-users] Obtaining bytes per second

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:
> I think the idea is to be explicit. I would just use something like
>
>   # Vecs * Vec size * 8 bytes/double + <same for Mat>
>
> and forget about small stuff. This model is uncached, 

This is for a perfect cache model -- each byte of the data structures
needs to be fetched from DRAM only once.

Make sure that "# Vecs" actually means the number that are accessed.
For example, GMRES accesses an increasing number of vectors on each
iteration (until a restart).

> and you just state that up front. Someone else can take the data and
> produce a more nuanced model.
>
> You can use the Flop counts (not Flop/s) from PETSc,  and get a rough
> estimate
> of flop/byte ratio.

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