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Graphics
Geforce PhysX is heavy on the CPU
Ageia PhysX isn’t
With the latest Nvidia drive to make people jump onboard the PhysX bandwagon, we did a quick and dirty test with the help of Nvidia’s own particle fluid demo. We actually have a PCI PhysX cards from the days of Ageia and we thought it’d be interesting to put it up against a Geforce card to see how both perform against each other.
There were a few unexpected surprises that we ran into; first of all we noticed that the Ageia solution was unable to render as many fluid particles as the Geforce option, which in this case was a Geforce 8800GT. In fact, it couldn’t even do half the amount of fluid particles that the Geforce 8800 GT card was able to do.
Now this might just have been down to faster hardware, but we noticed that the render was stuttering on the Ageia hardware and we couldn’t quite figure out why, as this wasn’t an issue when using the Geforce PhysX option in the drivers.
Running Fraps revealed that the Ageia card only managed about 15fps while the Geforce 8800GT was doing on average about 24fps. Again, we simply put this down to the Geforce solution being faster. Then we happened to glance over at the CPU usage widget in Windows Vista and noticed that there was a massive difference in CPU usage between the two.
The Ageia card only used between 30 to 40 percent of the CPU, taking into account that at idle at the desktop about 20 percent of the CPU is being used. Switching to the Geforce 8800GT the CPU usage jumped up to between 75 to 80 percent and at times even higher.
Even running the demo in pure software mode doesn’t use as much CPU as the Geforce PhysX option, although the demo is vastly slower using the software mode, which relies purely on the CPU. Oddly enough the software mode would produce the same amount of fluid particles as the Geforce card, no matter if the Geforce or Ageia option was ticked in the drivers.
This makes us wonder if Nvidia is playing fair and square, does the GPU actually do all the PhysiX calculations or are Nvidia offloading a whole bunch of calculations onto the CPU. Is this just a demo issue, or is there something more to this? At this moment we don’t have an explanation as to what is going on, but we’re sure that we’ve just stirred up yet another hornets’ nest.