A personal record of understanding, deciphering, speculating and predicting the development of modern microarchitecture designs.

Friday, December 31, 2010

AMD Bobcat Fusion APU -- A Big Deal?

AMD has been enthusiastic and optimistic about its upcoming Fusion Accelerated Processing Unit (APU) based on the Bobcat cores set for launch at next year's (really less than one week from now) International Consumer Electronics Show (CES) in Las Vegas. It even makes a supposedly humorous video on YouTube, showing its main competitor spying on and astonished by AMD's "Fusion technology".

Is the Fusion APU really a big deal and, if so, in what sense? Will it really revolutionize personal computing as claimed by AMD?

The Facts

We already know the performance bound of these Fusion APUs, straight from AMD: compared to current CPU designs, the Bobcat core will achieve 90% performance with 50% die area. So a 1.6GHz Bobcat core will have performance comparable to a 1.4GHz Turion, definitely not a stellar specification. In fact, the APU's performance has been previewed and shown to be comparable to Intel's CULV CPU + nVidia's ION GPU.

The more impressive part is perhaps that the APU has both the CPU and GPU sitting on the same die, sharing the same system interface and 18W power envolope. Thus from the performance perspective, APU is much better than Intel's Atom processor (which powers most of the current low-cost netbooks), while from the power and cost perspective, APU is much better than Intel CULV + nVidia ION. So the whole point of these Fusion APU is really not about better performance (in both processing speed and power), but to reach a "better" power-performance tradeoff, i.e., performance-per-watt.

The Advantage

But is this power-performance tradeoff the real "advantage" of the Fusion APU, that it is unreachable by other players? I highly doubt it. For example, if one combines Intel's Yonah and nvidia's ION2 and manufactures them on Intel or TSMC 32nm, the same level of performance-per-watt could very well be reached.

However, even if Intel and nVidia work together, such a product probably won't make money for Intel due to all those redesign efforts required and the erosion to Intel's existing products. So IMHO one critical "advantage" that AMD has with APUs is that AMD's current market share in low-power laptops is so small that it doesn't worry about cannibalization by releasing cheaper products. Intel OTOH doesn't want to replace their existing laptops with lower performance cheaper ones. Instead they designed Atom to target on the smartphone and tablet markets. They make sure there's significant performance gap between Atom and Core i3 so the two markets are well separated.

The Extra

Hardware is only part of the story. By combining CPU and GPU closely together, every laptop based on AMD's Fusion APU becomes DirectCompute and OpenCL capable. Such "universal" GPGPU availability makes GPGPU acceleration a viable choice for software developers, which in turn makes these Fusion APUs better products (since more programs will be optimized for the CPU+GPU package). OpenCL came along somewhere in 2008 is an industry standard that replaced the original ATI Stream. Kernel programming in OpenCL is also very similar to that in nVidia CUDA, making OpenCL a fine choice for developers who are looking for or already taking advantage of GPGPU.

The "Better" Product?

However, even with GPGPU acceleration, a 18W APU still won't achieve stellar performance. Do you really believe the 18W TDP can translate to personal supercomputer, artificial intelligence and immersive 3D interface? What would be more interesting instead is the Fusion APU with the Bulldozer CPU core and the "Southern Island" GPU. That plus OpenCL could really be revolutionary in terms of software acceleration. But that plan, first disclosed by AMD in 2007, had been delayed until at least 2012/2013. Instead, Bobcat-based low-end Fusion APUs came to fill the void for the next 1 to 2 years.

While the current Fusion APU is not in AMD's original plan, with some irony it is probably a "better" product than originally planned. Why? Because believe it or not, most laptop users really don't need higher CPU performance! Most people will be quite happy with a dual-core 1.6GHz computer which they use mostly for e-mail and web surfing. The good graphics offered by these APUs is just a sweetening plus.

So what AMD does with the Bobcat-based APU is to depress CPU+GPU prices and power budgets so laptop makers can give us better other stuff, such as longer battery life, better webcam, and faster WiFi/3G/4G. And although this Fusion APU will reduce CPU+GPU ASPs and will hurt high-end laptop sales, AMD has little to lose in those areas anyway. :-)

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