Nvidia unquestionably uses PhysX as an exclusive marketing tool for their GPUs, and it clearly benefits from executing on a GPU. Nvidia claims that a modern GPU can improve physics performance by 2-4X over a CPU. That’s a pretty impressive claim, and some benchmarks (e.g. Cryostasis) seem to bear that out. However, detractors of Nvidia (largely those working at one of Nvidia's competitors) have repeatedly claimed that PhysX purposefully handicaps execution on a CPU to make GPUs look better.

Of course, comments from a competitor should be taken with a large grain of salt. But if Nvidia does cripple CPU PhysX, it would throw into question the extent to which GPU PhysX is really beneficial. Certainly a 4X advantage is worth while. However, if the CPU is really hobbled and runs 2X slower by design, that would mean that the GPU only has a 2X advantage in reality, which is far less impressive.

A couple months ago, we decided we would profile a couple of applications which use PhysX to test how PhysX behaves on the CPU and GPU. Initially, we were going to use VTune to compare, contrast and analyze both GPU accelerated and CPU PhysX by collecting performance counter data. However, after we first ran the experiment with VTune to analyze PhysX execution on the CPU, our results were so strange that we changed our plan to focus solely on profiling CPU PhysX and examine how it is tuned for the CPU.

Read the entire article in Real World Technologies.