Multi-core in the Source Engine

The benchmark

To help illustrate how Source is handling multi-threading, Valve provided bit-tech with a benchmark that applies multi-threading to the specific problem of particle physics.

What is particle physics? Well, it's the interaction of micro-elements within the game - smoke, water, rain, fire. Tom expands: "With multi-core, you can have more complicated systems. You can have smoke that drifts off, bounces off the ceiling and then out the door."

"Better, you can have particle systems that actually have gameplay implications. Currently, particle systems are a representation of a game state - something is on fire - but they are fundamentally disconnected from the game world. But how about this - suppose you had a game where you were a wizard, and there was a field on fire. You could be genuinely concerned that the embers flying off the fire in the wind might hit the scroll in your hand - the scroll that has the spell on it to summon rain, the drops from which realistically douse the fire. These kind of experiences re-enforce the consistency of the world."

We are told that the nice thing about particle systems is that they scale really well, and this makes them good for a benchmark. Chris Green, one of Valve's visual gurus, helped develop a benchmark to illustrate just that. The benchmark processes a number of particle examples and, depending on how quick it is able to do those, spits back out a number that is representative of performance.

Check out these two videos of the benchmark in action:

In the first video, you can see a rain particle effect, as droplets interact with each other, and with the water on the ground, realistically. The second video shows collision being done. The benchmark evaluates the ease with which the CPU can calculate these in-game and two further particle effects.

We ran the benchmark on our rock Xtreme CTX notebook, which has a T7600 Core 2 Duo CPU (running at 2.33GHz) and a 512MB 7900 graphics card. To test the scaling across multi-threading, we ran it with one core enabled and then two. The results speak for themselves - particle physics in Source scales pretty linearly, according to these results.

When we get back to the office, we'll be sure to run this over our Kentsfield system in more detail.