Effect of changing processor number

Unified Model
,
1

Hi,

When I was testing one my code modifications in UM12.0 in Archer2-puma2 for my research related work, I tried changing to the below processor numbers in the rose-suite.conf

MAIN_ATM_PROCX=26

MAIN_ATM_PROCY=24

compared to the original values of

MAIN_ATM_PROCX=24

MAIN_ATM_PROCY=21.

I have kept all other entries related to the processor numbers intact (OMP_ATM, PE_ATM, etc.).

This was to test if my code modifications has any dependence on the processor number configurations. But I did find some small changes in the model output. I was wondering if this is an issue with my code modifications, or you really expect the results to look slightly different when I make the processor number changes as above?

Cheers,

Timmy

2

Hi,

This behaviour depends on the model schemes.

If this is an UKESM type configuration with full chemistry then changing answers with PE setup is a known feature of the solver used.

On the other hand a GA/GC model without chemistry is expected to maintain the results for different PE setups. If this is not seen a bug has likely been introduced from a code change.

--

Mohit