Hello Erik, all, > You mean "counting the number of flops in a Hydro+AMR+Neutrino > simulation is quite hopeless". Counting in GR is not hopeless since > Kranc can do that for us. (Okay, it doesn't count the stencil > operations yet.) Well its worse than that really. Even *if* I had a small enough code (or code generator) so that I would try and consider the number of FLOPS for a point that is in the interior of the grid on a single level, ignoring buffer zones, ghost zones and the issue that some values are recomputed in buffer zones while others are interpolated, the hydro codes almost always have different code paths depending on the values on the grid (eg reconstruction or the Riemann solvers or the non-linear root finding in con2prim which is ~1/3 of the computational costs usually) so that number of FLOPs used for a grid point is not predictable unless one knows exactly what data will be present at the grid point.
So that best I can hope for is some rough estimate, which the counters on BW should give me. > Modern Intel CPUs don't have hardware counters for Flops any more, as This being BW, it's neither Intel nor strictly modern CPUs :-). But instead AMD Interlagos CPUs. My laptop on the other hand with a modern Intel CPU simply does not provide any PAPI numbers at all. > In other words, using a hardware performance counter to count > operations is about as accurate as counting steps to measure distance. > There's a correlation, but it's difficult to quantify the error. True. Yours, Roland -- My email is as private as my paper mail. I therefore support encrypting and signing email messages. Get my PGP key from http://keys.gnupg.net.
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