At Memcon today Mike Demler of the Linley Group (and coincidentally someone who used to work for me back at Cadence and who now run Memcon, small world) gave an interesting presentation on Trends in Mobile Processors. A mobile application processor (AP) is a highly integrated SoC to run the applications in a mobile device. Mostly they run Android or iOS although there are a few other mobile operating systems around. The AP always contains MMU, GPU, ISP and VPU but increasingly they might contain cellular baseband (typically LTE these days), Bluetooth, Wi-Fi and GPS although sometimes those are on separate chips. The power is 2W or less in a phone, 4-5W in a tablet.
Starting with Samsung’s Exynos Octa these often contain four main cores or up to 8 in the ARM big.LITTLE configurations. All cores get counted since all can be running at the same time (initially big.LITTLE could only run the big or the little out of each pair). The smallest cores are slower but consume a lot less power (and area). For example, Cortex-A7 is 3.5x more efficient in MIPS/W and 2x in MIPS/mm2.
But there is a dirty secret. When the Chinese smartphone test service Testin measure multicore utilization on a Qualcomm APQ8064 (it is a quadcore Snapdragon AP) the utilization was 58% on the first one (actually the zeroth one, computer scientists like to start counting at zero) was 58%, on core 1 it was 49% but on cores 2 and 3 it was 2% and 1%. The numbers vary a little with the benchmark but the basic fact remains true. Only two cores are really getting any use.
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So if 4 cores are not even being used then why 8 cores. Basically marketing. One thing that I’d not thought of is that in Chinese culture 8 is a symbol for prosperity (because it sounds like the word for wealth) and 4 only differs from the word for death in the tone. My ex-father-in-law used to work for Wedgwood and for the Chinese market they had to ship a tea-service, say, with 5 cups and saucers not 4. Some games can use 4 cores but the improvement over 2 is minimal.
So where are we? Single core is pretty much gone. Quadcore is the most common configuration, the average will be 4 next year. It is also all going to be 64-bit. Apple designed the first 64-bit ARM (before ARM) followed by Qualcomm (they both have architectural licenses so don’t have to wait to get the IP from ARM). Same for the Intel processors: quadcore Baytrail for tablets and quadcore Moorefield for smartphones (although so far only used for phablets). But again the transition is driven more by marketing than technology since it is not needed until devices with 4GB of DRAM appear. There is actually a performance advantage since A53 is faster than A7 even on 32 bit code and the area penalty is minimal.
Having written yesterday about Intel losing $1B/quarter in mobile, Linley’s projection is not optimistic that this will change. They predict rapid decline in 32-bit ARM APs, rapid growth in ARM 64-bit APs (A57 at high end and A53 at low end + Apple and Qualcomm doing their own thing) and nothing significant in x86.
Graphics will get a lot more powerful driven by games and the transition to what is called 4K video (4000 pixel horizontal resolution approx). The drive for this is not so much that phone screens will have that resolution but people will want to connect their phones/tablets to high-resolution TVs, if and when we have them (which remains to be seen).
Next week is the Linley Processor Conference on October 22nd to 23rd. I’ll be there (so will Mike Demler). It is in the Hyatt Santa Clara (yes, in the hotel not the conference center). Details here. This is not the mobile processor conference which is in the spring, this one is focused on networking and base-station. But note, registration closes at 5pm today.
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