Single core versus dual core performance

Comparison of single node versus virtual node mode shows that the runtime is generally faster when running in single node mode. The likely reason for this is that single node mode will create less contention for both memory and I/O nodes than running in virtual node mode. Table 2 shows the runtimes for 256 and 221 processors using a 16 by 16 grid for both single and virtual node modes. It should be noted that the 221 processor run has had the land only cells removed. The effect of removing land only cells will be examined in section 6.5.

Table 2: Runtime comparison for 60 time steps for single node (mppnppn=1) and virtual node (mppnppn=2). Runs were performed using the PGI compiler

jpnij	jpni	jpnj	Time for 60 steps (seconds)
			mppnppn=1	mppnppn=2
256	16	16	119.353	146.607
221	16	16	112.542	136.180

From table 2 we can see that single node mode is up to 18.59% faster than virtual node mode. As the charging structure on HECToR is per core, single node mode will cost significantly more (almost double) AU's than virtual node mode. Thus, running NEMO in single node mode should only be considered if it's critical to obtain a fast solution.