fog wrote:After reading this complete thread several times and checking other ressources regarding hardware for WRF, it seems clear to me that you have to find a good balance between CPU performance and RAM performance.
What I ask myself now, especially after reading that going from single channel ram config to dual channel config makes a huge difference:
Wouldn't it be best to give each physical core his "own" RAM channel, so none of the cores has to fight for memory access?
That is what is NUMA about (numad daemon on Centos) and this works and has sense only in multisocket environment whare you limit access to memory controller of particualar CPU socket. It would have no difference on single socket computers.
As I understand intels i7/xeons, you are limited to four RAM channels per physical processor at the moment, so this would be my first (naive?) configuration:
one fast quad core CPU with four RAM channels, 4(8) RAM sticks (single socket system)
two fast quad core CPUs with four RAM channels each, 8(16) RAM sticks (dual socket system)
fog wrote:Regarding raw computing performance (ignoring disk I/O for now), it seems to me that WRF can't benefit from CPUs with >> 4 cores, given a reasonably fast CPU (3-4GHz?).
It can because not all computing is done through northbridge (CPU-RAM path), but also in CPU cache, which means that more computing cores you have, you will always get faster computing, at least in theory. However, computing speed won't increase linearly with adding more cores, but more logarithmically.
fog wrote:I know that eventually I have to run benchmarks on different configurations to find out, but as dual socket xeons with 20 cores are quite costly at the moment, I appreciate every comment!
The best you can do with multi-CPU computers it to make sure memory configuration is fastest you can get. This usually means populating all memory banks with chips to achieve "performance mode", but you need to consult user manual of particular computer. Also make sure that you use latest generation hardware if you can, because every next generation is ~10-20% faster than previous, given the same number of cores and frequency.
Sure, if you can't afford too much costs, one socket I5/I7 systems of latest generation is safest choice and has best overall performance/price ratio for WRF.