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5 July 2022

ARM leverages ray tracing to push its Mali GPUs up the performance scale 

ARM debuted its new Immortalis range of graphical processing unit (GPU) designs with a refreshing lack of metaverse hype, despite including a virtual reality interview with John Romero of Doom fame (the video game).  


There is now a new trio of GPU designs, with a flagship tier called Immortalis. While the Mali G615 and G715 GPUs will be notable upgrades on their predecessors, the Immortalis G715 is meant to be a step above what used to be the top dog. 


However, at first glance, in the datasheet comparison, the Immortalis version appears identical to the Mali G715 – with only its support for ray tracing marking it out as different. However, while the Mali G715 is a 7-9 core design, the Immortalis is intended for 10-16 cores. As such, the Immortalis is going to be found inside the most powerful system-on-chip designs, likely flanked by a suite of CPUs including ARM’s shiny new Cortex-X3. Last year saw the debut of the v9 CPU architecture, and its associated performance improvements, and now the GPUs are getting a buff too. 


It was no surprise to see gaming be the focus of the announcement, but ARM’s general manager for the client line of business, Paul Williamson, hinted heavily at future devices that might need these powerful GPUs. AR/VR, and mixed reality (MR) are all on the table, but the lead time for taking these new GPUs all the way through to production means that we will not be seeing them for a couple of years. 


Romero’s pre-recorded interview outlined how the jump from Wolfenstein 3D to Doom, between 1992 and 1993, using “two-and-a-half-D”, triggered an explosion in the gaming industry – partly because id Software had given away the data models needed to build games engines. With Quake appearing in 1996, we saw the first fully 3D videogame. 


The subtext to the discussion was that the arrival of AR, VR and MR is poised to trigger another similar explosion in development. With Immortalis, the focus will be on how ray tracing can be used to create immersive virtual environments, using the new light-modelling technologies to better convince people that they are in a real location. 


The current approach to modelling light is effectively a series of fixes piled one on top of the other, over the past 25 or so years. Essentially, you need to be able to provide accurate shadows for objects in the virtual environment, or our brains will not be convinced. 


However, the previous approach required modelling a scene in extreme details, to know where all the sources of light were in the 3D space. Once that was done, the shadows could be put in the right places, with all the extra work of reacting to people moving in front of lights, or passing torches over darkness, or explosions going off, and so on. 


With ray tracing, the promise is that the light will just work – that you will only have to model the light sources in an environment and the technology will do the rest. The likes of Nvidia and AMD have discrete GPUs for PCs that have ray tracing capabilities, but these are not suited for the mobile sector due to their power draw and consequent heat output. 


This is where ARM is making its play, building on its mobile heritage to bring these next-gen graphics capabilities to smartphones first, and later to new AR, VR and MR devices. As with many software functions, creating dedicated hardware designed to only do those functions usually enables much greater power efficiency, and so the Immortalis GPUs promise to set the stage for a new type of mobile experience. 


The Vulkan API is being used for ray tracing here, and ARM reckons the hardware approach provides a 3x improvement over the software-only approach. Given that MediaTek was highlighted in the pre-recorded session, it seems sensible to expect that the OEM will be one of the first to use ARM’s first ray tracing hardware in a phone. 


In the presentation, ARM made reference to the need to use 64-bit processing if you are serious about performance. This begs the question of how many flagship phones are still stuck on 32-bit architectures, and Williamson did note that ARM has committed to moving to 64-bit only, and that the major Chinese app stores have moved things along appropriately. “This is the first year that we expect the highest performing devices to all be 64-bit,” said Williamson. 


Another question probed the level of current developer support for ray tracing. Williamson pointed to a recent demo with Oppo, which focused on software-based ray tracing features, and said that developer support is growing. ARM has been working with Unity on this point, and the goal is to implement new APIs to make use of the hardware features, to make the developer experience as seamless as possible. 


ARM is not ruling out its designs being used in a discrete GPU design. Williamson also said that while Immortalis has been heavily tuned for mobile, it is possible it might make an appearance in the data center. 


Notably, ARM has been working closely with Microsoft for the Windows-on-ARM projects, which were mentioned in the announcement, with ARM-based laptops looking set to benefit from an increased interest from Microsoft. Given the performance improvements that Apple has enjoyed since abandoning Intel’s x86 designs in favor of its inhouse ARM platform, Microsoft is likely nudging its ecosystem in the same direction.