ARM’s new CPU and GPU will power mobile VR in 2017

May 30, 2016 by in category 2017, ARM, CPU, GPU, Virtual Reality tagged as , , , , , , with 0 and 0
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ARM, the company that designs the processor architectures used in virtually all mobile devices on the market, has used Computex Taipei 2016 to announce new products that it expects to see deployed in high-end phones next year. The Cortex-A73 CPU and Mali-G71 GPU are designed to increase performance and power efficiency, with a particular view to supporting mobile VR.

ARM says that its Mali line of GPUs are the most widely used in the world, with over 750 million shipped in 2015. The new Mali-G71 is the first to use the company’s third-generation architecture, known as Bifrost. The core allows for 50 percent higher graphics performance, 20 percent better power efficiency, and 40 percent more performance per square mm over ARM’s previous Mali GPU. With scaling up to 32 shader cores, ARM says the Mali-G71 can match discrete laptop GPUs like Nvidia’s GTX 940M. It’s also been designed around the specific problems thrown up by VR, supporting features like 4K resolution, a 120Hz refresh rate, and 4ms graphics pipeline latency.

As for CPUs, ARM is announcing the new Cortex-A73 core, which prioritizes power efficiency. It’s up to 30 percent more efficient than the previous Cortex-A72 while offering about 1.3 times the level of peak performance, but ARM has also focused on sustained usage — the A73 offers over twice the performance within its power budget, meaning it doesn’t need to be as hasty to slow down to save battery life.

Although ARM architecture dominates the mobile landscape, there’s a good chance you won’t see these specific products in your 2017 flagship phone. ARM licenses its architecture and cores separately, meaning companies are free to pick and choose what they like. Apple, for example, licenses ARM architecture but now designs its own custom CPU cores (known as Twister in the most recent A9 processor) and uses PowerVR GPU solutions from Imagination Technologies. Samsung, meanwhile, designs some Exynos processor cores but uses them alongside ARM’s Cortex cores and Mali GPU in the international Galaxy S7. And Qualcomm reverted to its own custom Kryo CPU cores in the Snapdragon 820 — which powers the US Galaxy S7 — after using Cortex in the 810.

All of this is to say that you shouldn’t take the performance laid out here by ARM as a benchmark for your next phone, because it’ll all depend on how the manufacturers choose to implement the technology. But the new Cortex and Mali products do demonstrate that mobile technology continues to advance in terms of power and efficiency, and that it’s adapting to new challenges such as VR.

ARM expects chips to move into production at the end of the year and appear in shipping devices in early 2017.

Many companies, Apple, Samsung, and Qualcomm included, like to rely on their own custom ARM CPU architectures for their chips, but the CPUs and GPUs that ARM itself designs for other companies to use are still important. They let commodity chipmakers like MediaTek and Rockchip offer chips with good performance for less money, and they serve as a sort of pace car for the rest of the mobile industry.

Enter the new Cortex A73 CPU architecture and the Mali G71 GPU. These are new high-end designs that target 2017’s flagship phones and tablets, but they’ve also been designed with virtual reality and augmented reality in mind.

Cortex A73: A new “big” core


Cortex A73 is being positioned as a replacement of sorts for Cortex A72, which in turn replaced Cortex A57. Like its two predecessors, it’s a high-end 64-bit CPU design, and it can be paired with with “little” Cortex A53 or A35 cores that handle light or idle tasks to reduce power consumption.

ARM says that A73 will improve performance by 30 percent while “increasing power efficiency” by 30 percent. Some of that speed increase comes from a clock speed bump—ARM’s figures compare a Cortex A72 running at 2.5GHz to an A73 running at 2.8GHz—while the rest comes from architectural improvements. And at least some of that power efficiency will rely on new 10nm processes from the likes of Samsung and TSMC; today’s chips are being made on 14nm or 16nm processes.

10nm parts should be ready to ship by early 2017, when ARM says A73 will begin to show up in consumer devices, but we may see some A73 SoCs built on the more mature 14nm or 16nm processes. Beware of that when it comes time to measure A73’s performance in the real world.

New CPUs are expected to improve performance and/or reduce power consumption, but ARM also had another goal for A73: improving sustained CPU performance. As we’ve examined elsewhere, mobile processors in particular are designed for “bursty” usage. You whip your phone out, poke around at a few apps, and put it away. As a result, most mobile chips are designed to run at high clock speeds for short amounts of time, but they have to ramp down quite a bit if you’re pushing the hardware for an extended period of time (games are the best real-world example of this, but as phone and tablet apps become more varied and capable, it’s going to come up in more and more places).

ARM says that Cortex A73 CPUs ought to be able to perform at peak levels for much longer than A57 or A72 CPUs could—it’s not clear what activities ARM is using to measure this or for how long they’re running, but it’s interesting that ARM is talking about sustained performance at all, given that the focus is usually on peak performance. To date, Apple is really the only smartphone maker that has bragged about its sustained SoC performance.

Good sustained performance is especially important for VR and AR. Both applications are sensitive to dropped frames and inconsistent performance, and developers need to be able to make assumptions about how well the hardware will be able to perform when under load for extended periods of time. Android N even includes a “sustained performance mode” intended to smooth out performance and keep throttling from becoming an issue. As peak performance gains become harder to come by—an inevitability, if desktop and laptop CPUs are any indication—expect more OEMs to start talking about sustained performance and focusing on VR as much as they focus on general app and game performance.

Maii G71, and the “Bifrost” GPU architecture


Mali G71 is ARM’s new high-end GPU, and it’s built on a new architecture called “Bifrost” that will eventually trickle down to lower-end parts as well. ARM says that the GPU architecture is its “most scalable GPU to date,” and that it eliminates overhead present in the older “Midgard” architecture.

On the API side, Bifrost doesn’t enable G71 to enable anything that current ARM GPUs can do, at least not yet. It was built with the low-overhead Vulkan API in mind, but Mali T600-, T700-, and T800-series GPUs can all support Vulkan just fine provided they get the necessary driver and OS updates from OEMs.

The more significant advancement is support for HSA, which is important for GPU computing. HSA allows the CPU and the GPU to access the same data in system memory at the same time, which eliminates overhead since the two no longer have to work with two separate “pools” of memory. The CPU and GPU can each work with the data it’s best suited to without having to wait for things to be copied between those memory pools.

Compared to a Mali T880 GPU on the same process node, ARM promises that G71 will deliver 1.5 times the graphics performance, thanks to energy efficiency, performance density, and memory bandwidth improvements. The number of shader cores doubles from 16 to 32, though lower-end GPUs with fewer cores will surely begin to appear in the months after G71 launches.

These improvements come primarily from reducing overhead; a new “quad vectorization” system can execute four threads at once, making more efficient use of the GPU hardware and leaving less of it idle during any given operation. And using “clause execution” to schedule multiple instructions at once without having to pause before and after every individual instruction also reduces overhead.

ARM says that SoCs using Cortex A73 and the Mali G71 GPU will enter production in late 2016 and be available in actual devices in early 2017. The GPU technology will trickle down to lower-end chips, but ARM isn’t upgrading its low-end CPU architectures. Cortex A53 is still the company’s go-to low-to-mid-end 64-bit CPU architecture, while truly low-power SoCs can use Cortex A35 instead. Both of those cores can be combined with different numbers of A73 CPU cores to create high- and mid-end chips depending on how fast you’d like your chip to be.

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