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AMD Fusion: What Can It Do?

AMD Fusion: Brazos Gets Previewed: Part 1
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If you haven’t yet seen our earlier coverage of AMD’s 2011 Code Names, its a good time to play some catch-up.

Fusion: AMD is using the word Fusion to describe an approach to processor design and software development, in its words: “…delivering powerful CPU and GPU capabilities for HD, 3D, and data-intensive workloads in a single-die processor called an APU (accelerated processing unit). APUs combine high-performance serial and parallel processing cores with other special-purpose hardware accelerators, enabling breakthroughs in visual computing, security, performance-per-watt and device form factor.”

In short, an APU designed according to AMD’s Fusion initiative will include a CPU and a GPU on a single piece of silicon. The improvements an APU are supposedly going to deliver include enhanced mainstream gaming performance and accelerated video transcoding, to name a couple of specific examples.

Fusion is the culmination of the AMD and ATI merger. AMD sees this as the next step in processor design as we near the apogee of the “Multi-Core Era.”

Remember that any system is only as fast as its slowest link. This means computational bottlenecks are always going to be a mix of bandwidth and latency. AMD considers its APU a Heterogenous Processing Unit, since it introduces a massive SIMD GPU array that allows general use programmable scalar and vector processor cores. This means that, while the GPU consumes the greatest real estate on the die, APUs will benefit from parallel processing capabilities particularly, as the shared memory helps enable lower latencies that integrated graphics processors have never enjoyed.

Discrete GPU solutions clearly still have their place, but APUs will still offer a big boost to value-oriented customers compared to anything seen from AMD before.

The real question becomes: how can Fusion speed up everyday tasks? Even if the processor cores are on par with what we see today, what can that on-die GPU do? We had a discussion with Tom Vaughan, CyberLink’s director of business development about this very issue. His company's software is quite often at the forefront of supporting brand new hardware technologies. Looking to the future, CyberLink sees a time when the capabilities of an APU and a discrete graphics solution are additive through an API like OpenCL. For example, if you have an APU with 400 stream processors and an add-in card with 1600, there could be gains tied to using them cooperatively. Or say you're running your display from the on-die graphics, and only spinning up the discrete card when a 3D application needs it. There might be power-oriented benefits there.

More immediately, though, you should be able to operate an APU and see near-identical performance to a comparable CPU/discrete graphics solution. Taking the PCI Express bus out of the equation does cut down on some latencies, but you'd be hard-pressed to tell either configuration apart. The real gain stems from the integration. Putting one more (capable) subsystem into the processor eliminates a discrete card, which in turn cuts back on cost, power, and motherboard complexity. This is really about doing the same job for less money than it would have cost previously. Surely, that's one of AMD's hallmarks. 

In the past, the integration of graphics was a value-add that companies like Intel tried to sugarcoat. The reality was that only a subset of its customers could use the built-in graphics. Everyone else needed an add-in chip from a vendor like AMD or Nvidia. And when it comes to mobility, we all know what building with a discrete GPU does to cost. Now, integrated graphics is relevant to a far larger customer base. There is still a point where an add-in chip becomes necessary to support the habits of a more hardcore user. But that threshold shift to the right, as the diagram below illustrates. Atom cannot achieve that today.

Even though we are only looking at Brazos today (it’s a mainstream value platform), there are very clear performance benefits associated with optimizing for an architecture designed under Fusion's charter. When we get to look at Sabine and Lynx, things will look at lot more exciting, and the benefits of a beefier APU will become clearer. We’ll talk more about Sabine and Lynx soon enough, but today is, again, about Brazos.

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