[petsc-users] Make stream

[Jed Brown]

Fande Kong <fdkong.jd at gmail.com> writes:

> Hi All,
>
> I am trying to interpret the results from "make stream" on two compute
> nodes, where each node has 48 cores.
>
> If my calculations are memory bandwidth limited, such as AMG, MatVec,
> GMRES, etc..

There's a lot more to AMG setup than memory bandwidth (architecture
matters a lot, even between different generation CPUs).  MatMult and
Krylov are almost pure bandwidth.

> The best speedup I could get is 16.6938 if I start from one core?? The
> speedup for function evaluations and Jacobian evaluations can be better
> than16.6938?

Residual and Jacobians can be faster, especially if your code is slow
(poorly vectorized, branchy, or has a lot of arithmetic).

Are you trying to understand perf on current hardware or make decisions
about new hardware?