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Message: <blockquote data-quote="ibnanv" data-source="post: 18259540" data-attributes="member: 218596">ARM details its upcoming Cortex-A72 microarchitecture<img src="http://www.extremetech.com/wp-content/uploads/2015/04/Cortex-72-348x196.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" />         Earlier this year, ARM announced its Cortex-A72 — a new custom  microarchitecture from the CPU designer that builds on and refines the  64-bit Cortex-A57. Ordinarily it takes up to 24 months for new ARM cores  to come to market, after the company announces a new CPU design. But  Qualcomm has told us to expect Cortex-A72 cores by the end of the year. If true, that would make this one of the company’s fastest CPU ramps, ever — so what can the new core do?If ARM hits its targets, quite a lot.New process, new productThe  Cortex-A72 is based on the Cortex-A57, but ARM has painstakingly  refined its original implementation of that chip. The company is  claiming that the A72 will draw 50% less power than the Cortex-A15 (a  notoriously power-hungry processor) at 28nm and 75% less power at its  target 16nmFF+ / 14nm process node. Compared to the Cortex-A57 at 28nm,  ARM still expects the A72 to draw 20% less power.<img src="http://www.extremetech.com/wp-content/uploads/2015/04/Cortex-Power-640x365.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /> ARM  is supposedly aiming for the Cortex-A72 to be capable of sustained  operation at its maximum frequency, which is a topic we touched on  yesterday when covering the Snapdragon 810’s throttling problem.  The CPU is targeting improved performance of 1.16x to 1.5x over the  Cortex-A57, clock-for-clock. Making this happen required revamping the  branch predictor, cutting misprediction by 50%, and a 25% reduction in  speculation power consumption. The chip can also bypass its branch  predictor completely in circumstances where it is performing poorly and  save additional power in the process.The Cortex-A72 is still  capable of decoding three instructions per clock cycle, but apparently  adds some instruction fusion capability to increase efficiency. Each of  these components has been power-optimized as well. AnandTech reports  that ARM’s dispatch stage can break fused ops back into micro-ops for  increased execution granularity, effectively turning a three-wide  decoder into a five-wide machine in some cases.<img src="http://www.extremetech.com/wp-content/uploads/2015/04/Cortex-A72-1-640x357.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" />ARM  is also amping up its game in SIMD execution units. Instruction  latencies have been slashed, pipelines shortened, and cache bandwidths  boosted. There are no huge changes in organization or capability, but  the CPU core should see significant improvements thanks to these  adjustments. ARM has even managed to shave off some die size — the  Cortex-A72 is supposed to be about 10% smaller than the Cortex-A57, even  on the same process.<img src="http://www.extremetech.com/wp-content/uploads/2015/04/Cortex-A72-Perf-640x353.png" alt="" class="fr-fic fr-dii fr-draggable " style="" />Image Credit: Ars TechnicaArs  Technica reports that according to ARM, the Cortex-A72 can even beat  the Core M in certain circumstances. Such predictions must be taken with  a grain of salt — they assume, for example, that the Core M will be thermally limited (we’ve seen that this can vary depending on OEM design).  Tests like SPECint and SPECfp tend to be quite dependent on compiler  optimizations, and while the multi-threaded comparison is fair as far it  goes, ARM is still assuming that the Cortex-A72 won’t be thermally  limited. Given that all smartphones and tablets throttle at present, the  company will need to prove the chip doesn’t throttle before such claims  can be taken seriously.All the same, this new chip should be an  impressive leap forward by the end of the year. Whether it’ll compete  well against Apple’s A9 or Qualcomm’s next-generation CPU architecture  is another question.</blockquote>

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