HSA was not “unified” in the modern sense. It still required designating memory as gpu or cpu side and these implied different cache coherency rules that meant memory couldn’t actually be shared, by default. To actually share memory you had to use a special “garlic bus” that guaranteed visibility and ordering and massively slowed down performance. Similarly, it was also impossible for the gpu to see cpu memory unless it was pinned and tagged for a special “onion bus”, but at least this was relatively fast iirc.
In contrast apple actually has everything tied into a single unified space with a single controller that immediately makes all writes visible regardless of where the happen.
They’ve also got enormously more memory bandwidth to play with. M1 Max is close to PS5 in both shader configuration and memory bandwidth.
https://www.realworldtech.com/fusion-llano/3/
In contrast apple actually has everything tied into a single unified space with a single controller that immediately makes all writes visible regardless of where the happen.
They’ve also got enormously more memory bandwidth to play with. M1 Max is close to PS5 in both shader configuration and memory bandwidth.