Optimisation
Model Optimisation
The cost of the Stratosphere-Troposphere chemistry scheme in UKCA using the Newton-Raphson solver with the on-line photolysis scheme Fast-jX relative to the climate model HadGEM3-A is as follows:
| Model | PEs | OpenMP Threads | Time Elapsed (sec) |
|---|---|---|---|
| HadGEM3-A | 8x16 | 1 | 3798 |
| HadGEM3-A + StratTrop(N-R) + Fast-jX | 8x16 | 1 | 15602 |
| HadGEM3-A | 8x16 | 2 | 2328 |
| HadGEM3-A + StratTrop(N-R) + Fast-jX | 8x16 | 2 | 11730 |
On a 8x16 PE configuration and 1 OpenMP thread on the Monsoon facility or the Met Office's Power6 IBM (hpc1e/1f), UKCA and Fast-jX together add 310% to the cost of HadGEM3-A. However, with 2 OpenMP threads and no OpenMP compiler directives in UKCA, the relative cost of UKCA is even higher, adding approximately 400% to the cost of HadGEM3-A. Adding aerosol chemistry and UKCA-MODE aerosols will make it even more costly. Therefore, there is a clear need for optimisation.
As part of the HadGEM3-ES development project, currently being led by F. O'Connor, there are plans to do some optimisation work on UKCA. In particular, a more complete assessment of the model cost will be carried out and the potential speedup which may be gained from simple code re-writing, load balancing, and the use of OpenMP will be explored. The use of an alternative solver, such as a Rosenbrock solver, may also be investigated.
