High Bandwidth Cache

Apart from AMD’s other new architecture due out in 2017, its Zen CPU design, there is no other product that has had as much build up and excitement surrounding it than its Vega GPU architecture. After the world learned that Polaris would be a mainstream-only design that was released as the Radeon RX 480, the focus for enthusiasts came straight to Vega. It’s been on the public facing roadmaps for years and signifies the company’s return to the world of high end GPUs, something they have been missing since the release of the Fury X in mid-2015.

slides-2.jpg

Let’s be clear: today does not mark the release of the Vega GPU or products based on Vega. In reality, we don’t even know enough to make highly educated guesses about the performance without more details on the specific implementations. That being said, the information released by AMD today is interesting and shows that Vega will be much more than simply an increase in shader count over Polaris. It reminds me a lot of the build to the Fiji GPU release, when the information and speculation about how HBM would affect power consumption, form factor and performance flourished. What we can hope for, and what AMD’s goal needs to be, is a cleaner and more consistent product release than how the Fury X turned out.

The Design Goals

AMD began its discussion about Vega last month by talking about the changes in the world of GPUs and how the data sets and workloads have evolved over the last decade. No longer are GPUs only worried about games, but instead they must address profession workloads, enterprise workloads, scientific workloads. Even more interestingly, as we have discussed the gap in CPU performance vs CPU memory bandwidth and the growing gap between them, AMD posits that the gap between memory capacity and GPU performance is a significant hurdle and limiter to performance and expansion. Game installs, professional graphics sets, and compute data sets continue to skyrocket. Game installs now are regularly over 50GB but compute workloads can exceed petabytes. Even as we saw GPU memory capacities increase from Megabytes to Gigabytes, reaching as high as 12GB in high end consumer products, AMD thinks there should be more.

slides-8.jpg

Coming from a company that chose to release a high-end product limited to 4GB of memory in 2015, it’s a noteworthy statement.

slides-11.jpg

The High Bandwidth Cache

Bold enough to claim a direct nomenclature change, Vega 10 will feature a HBM2 based high bandwidth cache (HBC) along with a new memory hierarchy to call it into play. This HBC will be a collection of memory on the GPU package just like we saw on Fiji with the first HBM implementation and will be measured in gigabytes. Why the move to calling it a cache will be covered below. (But can’t we call get behind the removal of the term “frame buffer”?) Interestingly, this HBC doesn’t have to be HBM2 and in fact I was told that you could expect to see other memory systems on lower cost products going forward; cards that integrate this new memory topology with GDDR5X or some equivalent seem assured.

slides-13.jpg

Continue reading our preview of the AMD Vega GPU Architecture!