[Qgis-user] [QGIS-Developer] CPU L3 Cache Effect

[Greg Troxel]

Eric via QGIS-Developer <qgis-developer at lists.osgeo.org> writes:

> Apologies if this isn't the correct forum but I have a theoretical
> question that hasn't been asked before anywhere as far as I can tell.

It is the wrong forum; IMHO it belongs on the user list.

> I'm building a new computer for GIS, and trying to pick out a
> processor. AMD CPUs now have a version which includes an L3 cache
> which is 2-3x larger than normal. I'm wondering what effect this would
> have on QGIS performance, if any.
>
> Logically, I would think that this could be a big advantage in the
> same way that more RAM is, but I don't understand the inner workings
> of QGIS well enough to say for sure whether it would be worth the
> added investment.

I asked my crystal ball about:

  - which CPU you are referring to (as in model #
  - which CPU you might use instead if you don't go for high L3
  - costs
  - the rest of your computer design, including SSD and RAM
  - total costs
  - what kind of things you do with qgis
  - the kind and sizes of your data
  - whether this is professional or hobby, and the labor rate you are
    using to offset labor and capex

While my crystal ball gives great answers, unfortunately the TOS
prevents me from disclosing them, but the overall answer is that there's
a 60% chance it's worth it.


But seriously, viewing "qgis" as a workload for benchmarking doesn't
make sense.

If you want to figure this out, you're going to have a to do a lot of
work.  I'd run the workload you want on the biggest computer you have
now, and vary the workload size to be able to graph speed vs size, and
see how the changes in that graph line up with cache sizes.  That should
give you a guess as to how much data you can fit in a given L3 size.

You've asked a question nobody can answer, and if you posted the details
of the computer you are thinking of, with two possible CPUs, and prices,
and also the details of workload (type of dataset, sizing), then you'd
at least help somebody else think about computer planning, and you'd
probably get some useful comments.