PinAffinity - A simple CPU affinity setter for virtual pin cabs

This is a very simple CPU affinity tool for Windows, designed specifically for virtual pin cab PCs. The goal is to provide a the basic CPU affinity controls most useful on a pin cab, with minimal user effort for configuration.

CPU affinity is one of the more useful tools on Windows for improving video game performance (and virtual pinball is fundamentally a video game), but it's probably also one of the lesser used tools because it's not all that accessible in the standard Windows tool set.

The way to use CPU affinity to improve gaming performance is to partition the CPU cores into groups assigned to "gaming" and "everything else". This gives the game software almost exclusive use of one or more designated cores.

The reason this helps is that it can reduce latency in scheduling game threads. The tricky thing to understand here is that we're not talking about CPU cycles or how high the "% CPU" meter is reading for a given core. What we're concerned with here is scheduling latency. That's the amount of time it takes for Windows to get around to resuming a suspended thread when that thread is ready to run again. For general software, that latency figure isn't very important, because what most software cares about is overall throughput - how many CPU cycles the program is getting, averaged over the long haul. But that long-term averaging doesn't work well for video games. For video games, it's very important to do each individual video update and physics model update at exactly the right moment, so that the video animation is smooth and matches up with real time. That's why latency is so important for video games. When a video game thread is ready to run, it's critical that Windows runs it right away.

How does core affinity help with this? It helps by letting you give the game program more or less exclusive access to a given core, so that Windows won't have to accommodate other program threads running on the same core. Keeping a given core free of non-game threads makes it more likely that the core will be free for the game's use whenever the game is ready to do a little bit more work, such as a video update. That in turn improves the chances that the game can complete frame rendering in time for each video refresh and can update the physics model in time for the next graphics render pass.

PinAffinity is designed to make it easy to achieve partitioning like this. First, it applies default CPU core affinities to every process running throughout the system (system permissions permitting; some Windows background tasks are protected against this sort of meddling even with "Run as administrator" privileges). Second, it lets you designate selected programs as members of the Pinball group, and it assigns these programs a different set of affinities. All affinity settings are persistent: the program continuously monitors the system for newly created processes, and assigns each newly created process to the designated affinity group. There's no need to do anything manually during normal operation - just launch the program at system startup and leave it running in the background, and it'll take care of setting the desired CPU affinities as processes come and go.