Originally Posted by victorijapoosp
Originally Posted by mistercrow
Its a unified pool of memory, its not unified memory.
The memory must be tagged and split as either Video Ram, or CPU ram. YOu can use it as "shared" but the performance penalty is apparently awefull.
Cerney actually talks about a unified pool. And yes its certainly more flexible than hard limits, but its still has to be allocated.
More crucial is how the 8GB of RAM in the PlayStation 4 is utilised. This unified pool is a significant advantage over platforms like PC and PS3, where CPU and graphics RAM takes the form of two entirely separate pools of memory. 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."
"One issue we had was that we had some of our shaders allocated in Garlic but the constant writing code actually had to read something from the shaders to understand what it was meant to be writing - and because that was in Garlic memory, that was a very slow read because it's not going through the CPU caches. That was one issue we had to sort out early on, making sure that everything is split into the correct memory regions otherwise that can really slow you down."