PCSX2 Documentation/Benchmarking Multithreaded PCSX2: Difference between revisions

As most people probably know, PCSX2 is primarily a dual-thread application.  The two main threads are described as such:

GS thread emulates the PS2's Graphic Synthesizer (includes texture swizzling, texture filtering, upscaling, and frame rendering)

Each thread relies on the other thread in some way -- the GS thread cannot swizzle texture data until the EE thread has uploaded said data, for example.  Meanwhile, the EE thread cannot upload texture data to the GS thread if the GS thread is currently bogged down rendering last week's frame to video.  During these periods, either thread will sleep, only to be woken up once the other thread has caught up in its workload.

In theory the act of sleeping the EE/GS threads should make benchmarking the CPU load registered by each thread pretty easy: all modern operating systems have built-in APIs for reading the busy/idle time of any thread on the system -- this is the same API used by your tried and true task/process manager, for example:

The solution to this problem is to use a more traditional method of manual load checking: timing various sections of code executed in-thread via either the aforementioned rdtsc (timestamp) or QueryPerformanceCounter, read at key points in the GS thread's execution/program flow.  This wasn't such a great idea a few years ago, due to K8/Athlon and P4 generation CPUs lacking a stable internal clock counter.  Fortunately, all modern CPUs have a consistent counter suitable for benchmarking, so the pitfalls that have been long associated with using Intel/AMD timestamps are finally obsolete enough to not be a concern for us here.