A pretty interesting article just appeared on Eurogamer detailing the porting process (from PC to PS4) of Ubisoft’s upcoming open world racing game “The Crew”.
In the article, developer of The Crew (PS4 version) stated that Playstation 4’s memory subsystem has two separate buses, one for CPU (Bandwidth: 20GB/S) and one for GPU (Bandwidth: 176GB/S).
The developer also revealed that allocating data correctly between the CPU and GPU bus is extremely important in order to achieve good performance.
Here are few quotes of The Crew developer from Eurogamer article:
“The PS4 operates a system where memory is allocated either to the CPU or GPU, using two separate memory buses.
“One’s called the Onion, one’s called the Garlic bus. Onion is mapped through the CPU caches… This allows the CPU to have good access to memory,” explains Jenner.
“Garlic bypasses the CPU caches and has very high bandwidth suitable for graphics programming, which goes straight to the GPU. It’s important to think about how you’re allocating your memory based on what you’re going to put in there.”
“The first performance problem we had was not allocating memory correctly… So the Onion bus is very good for system stuff and can be accessed by the CPU. The Garlic is very good for rendering resources and can get a lot of data into the GPU,” Jenner reveals.
What does this exactly mean?, If PS4’s memory pool is unified (which is confirmed by Sony) but the buses are separate and of different speeds. So the question simply arise here, Is the PS4′ memory subsystem truly unified?