p3 vs p4 for CFD: winner p3

Clif Upton

we've been benchmarking our new p4-2.26 GHz, 1 Gb DDRAM vs an older laptop with p3-800 MHz, 512 Mb SDRAM and vs a p4 1.4 gHz, 512 Mb RDRAM. All computers were by Dell.

We designed a suite of CFD problems of different size, with the largest requiring slightly more than 512 mb so that the p3 and p4-1.5 had to page a little.

The results are pretty amazing. If for smaller problem the CPUs scaled roughly proportional to the processor speed, e.g. p3-800 was ~2.6 times slower than p4-2.26, as the problem size got larger p3 became 2 times(!) faster than p4-1.5 and almost 50% faster than p4-2.26.

We tried to explain the performance of p4-1.5 by the smaller cache (256 vs 512 on the other computers), but what would explain a computer with a 3x slower processor and slower memory beating the brand new p4 is beyond comprehension.

Any ideas of experience?