Processor designers and consumers alike look to the big core, the top end MHz figure, and the number of big processors in the system when they evaluate devices like premium smartphones and tablets. What they don’t realize is that I’m the one running during most of the time the mobile applications cluster is awake, and I’m the one that will enable improvements in battery life even as delivered peak performance increases dramatically. It is high time that the LITTLE processor gets the respect and appreciation that is due.
I’m speaking not just for myself here, but for my close cousin the Cortex-A7. We’re built from the same DNA, so to speak, sharing the same 8-stage pipeline and in-order structure. We both consume about the same level of power on our respective production process nodes, and although I bring added performance and support 64-bit, we are both quite alike. We are 100% code compatible for 32-bit code after all. And yet we don’t get the respect we deserve. It is an injustice, really.
In high-end mobile devices, my cousin the Cortex-A7 is always telling me how everyone wants to hear about how fast the Cortex-A15 is in the system, how many Cortex-A15 CPUs are in the system, and how many MaliTM GPU cores are built into the SoC. They don’t even notice if there are four Cortex-A7 cores in the design capable of delivering plenty of performance – more performance than a lot of smartphones in the market today. They just expect battery life to improve without giving any credit to the LITTLE processor that makes it possible.
Well they will soon see… big.LITTLE processors are coming into the market next year, nearly sampling already, and the capability of the LITTLE processor will be in full view, let me tell you.
Oh, and another thing – in the enterprise space, what they call “big Iron” – there is almost no recognition of the worth of small processors there. Sure, new designs are considering LITTLE processors in many-core topologies with ARM’s CoreLinkTM Cache Coherent Network (CCN) interconnect, but look at the products that are deployed today – they are mostly based on big cores, the bigger the better. Nowhere is this more evident than in the server space, where IT managers brag about how big their server racks are. Just wait and see. New server processors are being developed based on ARM, where even my big brother the Cortex-A57 is about an order of magnitude smaller and lower power than the incumbent processors. I’m in a different weight class altogether, but I can hang with the big boys on total performance. Purpose-built servers using lots of Cortex-A53 cores can deliver even more aggregate performance in a given power and thermal envelope. But are we LITTLE cores getting much attention in servers today? No. Well just watch and see. In 2015 when the first Cortex-A50 series 64-bit processors are built for lower power servers, you won’t be able to help but notice that LITTLE processors can get key jobs done in a lot less energy.
So I may be the same size relative to my Cortex-A57 big brother as the Cortex-A7 is to the Cortex-A15, but OEMs and consumers better not underestimate me. I’ve been going through intensive work these past 2 years to build up my muscles in the places that count: my SIMD performance is way up thanks to the improved NEONTM architectural support in ARMv8 and a much wider NEON datapath. I can dual-issue almost anything. My memory system is also juiced up, as is my branch predictor capability. That’s how I can pack a bigger punch than Cortex-A9 at around a quarter the power in our respective process nodes.
That’s all I’m saying, man. You gotta respect the LITTLE processor.
Brian Jeff, Product Manager at ARM, is based in Austin. Brian focuses on the power efficient vector along ARM’s application processor roadmap, including the Cortex-A5, the newly introduced Cortex-A7, and other CPUs further down the roadmap. He has also focused on benchmarking, performance analysis, and power analysis for ARM CPUs and systems. Brian joined ARM 3 years ago; prior to joining ARM he spent time at Texas Instruments and Freescale Semiconductor in product marketing, product management, and applications engineering roles. He has an MBA from the University of Texas at Austin and a BSEE from Virginia Tech.
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