The Polaris Architecture & Its Performance

*Note: an earlier version of this preview indicated AMD is using a 16nm manufacturing process. While there has been no official confirmation, either a 16nm or 14nm node may be used. We apologize for this error.

In essence, Polaris is simply the name given to an updated core design which utilizes AMD’s Graphics Core Next architecture. But make no mistake about it; this version of GCN has been so thoroughly revised that it can’t be directly compared to the architecture’s first showing in HD 7000-series Southern Islands cards. Indeed, as with other GCN derivatives it follows the same baseline core layout but adds its own set of optimizations to those already built into the architecture through the Sea Islands (Bonaire and Hawaii) and Volcanic Islands (Tonga and Hawaii) product families.Like its forefathers, Polaris will incorporate additional upgrades that AMD has deemed necessary to handle next generation workloads so performance in 4K and virtual reality environments alongside support for advanced display formats are being given priority. Whether or not this is termed “GCN 1.3” or “GCN 2.0” is immaterial at this point; the Radeon Technologies Group simply wants us to focus upon the Polaris nomenclature and its potential impact upon the future of gaming.For the time being the real nuts and bolts details about what make the Polaris architecture tick is still being held behind closed doors but we do know a bit more about the areas of GCN AMD is updating and which will remain as-is.Let’s start with the strengths of their current GCN design since the core elements are still going strong years after its introduction. For all intents and purposes the basic rendering pathways and core layout will remain the same since the actual needs of next generation workloads aren’t fundamentally different from what’s currently around. There are however many efficiencies built into upcoming APIs like DX12 and Vulkan that AMD can take advantage of through the implementation of targeted architectural improvements while still maintaining excellent performance in legacy situations.One of the areas deemed in need to some attention is the primary graphics command stages which contains the Hardware Scheduler, Command Processor and Asynchronous Compute Engines. Here they’ve added a new primitive discard accelerator and hardware scheduler which are supposed to work in tandem to more efficiently route requests through the Global Data Share and onto the geometry processing elements.The Asynchronous Compute Engines (which were already enhanced in Fiji-based cores) also receive an upgrade to improve their throughput. This bodes extremely well for DX12 performance since those ACE’s have already proven to be a key differentiator between AMD’s current GPU designs and their NVIDIA counterparts.It looks like the Geometry Engines will get some attention as well. Since these processing stages live within the Shader Engines and contain the Geometry / Vertex Assemblers along with a dedicated tessellation unit in GCN-based cores, we can only assume this means improved tessellation and shader throughput. Once again though, the details about what’s been done aren’t being made public just yet.The main Compute Units haven’t been overlooked either. The Fiji architecture’s implementation of Graphics Core Next kept the number of SIMD cores and Texture Units per CU constant from the previous generation while physically increasing the quantity of CUs per Shader Engine. In order to further boost performance in these stages, Polaris implements some key efficiency improvements and pre-fetch algorithms.Rounding out the graphics side of this equation, AMD is looking at enhancing their memory compression algorithms and will be addressing L2 cache limitations. It should be noted that the Polaris lineup will contain parts both with and without an HBM interface. This makes sense considering High Bandwidth Memory adds significantly to any BOM cost so integrating it into mid-range or lower-end GPUs may not be financially possible.As we’ve already covered in previous articles, Polaris’ media engines and display outputs will be designed specifically for next generation formats. The current Fiji and Tonga architecture faced their fair share of criticism for not integrating support for at least HDMI 2.0 which limited their usefulness for UHD 4K TV’s. That’s about to change in a big way.Not only will Polaris have native support for HDMI 2.0a and DisplayPort 1.3 (enabling 4K/60 content) but the architecture will also incorporate engines for decoding h.265 main10 at up to 4K and encoding 4K h.265 content at 60FPS.In addition to all of the information we’ve already gone through, the Radeon Technologies Group gave us a quick preview of Polaris performance. Since this architecture looks to achieve a new benchmark in performance per watt, the focus of their presentation was to up-play what their cards could accomplish when competing against a similarly-performing NVIDIA card.In the example above, both the Polaris-based card and a stock GTX 950 were used on the same test system and achieved identical performance. AMD’s newest architecture was able to hit a much lower system power consumption number even though this was using extremely early hardware and immature drivers. This bodes extremely well for mid-level and low power applications but it also tells us very little about how well it can scale upwards.We had some additional time to pick the brains of some folks at AMD’s Radeon Technologies Group and they brought up several more enlightening points. Like Tonga and Bonaire before it, the Polaris architecture’s mid-2016 rollout will target mid-level performance, hence why the performance numbers you see above are being compared to a GTX 950. When it is first introduced, the first Polaris-based cards will be considered a type of pipe-cleaning product that tests a new architecture and will allow AMD to further refine their new manufacturing process.This actually meshes quite well with the revised timeline for the dual Fiji card previewed last year and then later delayed to Q2 2016. That means Polaris will live alongside the current Radeon product stack in the short term to mid-term. We also hope it can scale well enough to finally replace cores that have been constantly rebranded as AMD fights to keep their lineup at least looking “fresh” to buyers and their system builder partners. However, while there are still plenty of questions we need answered, upon first glance it looks like Polaris could really be something worth waiting for.