How is efficiency impacted by core count and processing power of CPU in Android devices?

Drsunil V June 17, 2014
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How do core-numbers and strength of mobile processor differ in delivering efficiency to Android user in general for Android devices?

  1. Oron J
    June 26, 2014 at 7:22 am

    All other things being equall (which they never are), a 2GHz CPU is twice as fast as a 1GHz model. A dual core CPU can carry out the same number of instructions in total as the 2GHz model, but only if the tasks are split between the cores (each thread can only run on a single CPU). In other words, as pure speed goes, a fast single core is probably faster than slower dual-core.

    In terms of multitasking, dual core is better. If a thread runs at full tilt and uses 100% of the processor's cycles, a single core CPU will become non-responsive, or may even crash. A dual core processor will be affected far less since the second core will continue to run normally, handling the household tasks, interface etc.

    Battery wise - I've already covered that earlier. A dual core processor at 1GHZ will use up at-most around twice the power of a single core CPU, and less if one of the cores is slowed down or shut down. A single core 2GHz CPU will use up four times the power of the single core version.

    • Dr.sunil V
      July 3, 2014 at 7:38 am

      Thanks. The doubts on this topic are dispelled

  2. Oron J
    June 17, 2014 at 11:33 pm

    It's difficult to give a single answer to this. It depends on the context, however, here are a few general principles in CPU design which may be relevant.

    • For a given design, the power requirement (and heat output) is proportional to the square of the the clock speed. For example, let's say you you run a particular cpu at 1GHz and it consumes 1w. Now run it at 2GHz and it will consume 4w (2 squared).
    • A low transistor count is generally very efficient both in energy consumption (few transistors...) and in "pass through" speed (think of it as a city with junctions, the more junctions there are, the longer it takes to get through). This is the principle behind the design of RISC chips such as the ARM. On the other hand, you can make particular tasks very quick by having a complex CPU chip (predictive branching, memory copy, long division in hardware, signal processing...). This is the principle behind CISC chips (e.g. X86). The trick is to find the balance for your specific application(s).
    • Multiple cores are theoretically efficient in two ways: (1) they allow you to increase processing power without the logarithmic rise in energy requirements mentioned above and (2) when the device is idle, you can switch off, or at least slow down, some of the cores. They can also (again, theoretically), get over certain other bottlenecks such as memory speed issues. The problem is that they need to be supported and well utilised by both the operating system and the specific application(s). To date, support for multi-core architecture for consumer devices is very basic. The operating systems (Android etc) support it, but not on any great scale, and very few applications actively take advantage of multicore CPUs. The result is that 2-3 cores can improve the "efficiency" of a device by using less energy than a single core processor, and they will tend to "snag" less (freeze periodically or slow down to a crawl). Above that the benefit is marginal, if at all. The same is also true for clock speed. Up to a point, speed is good, but if the clock speed is too high, the device will run hot and use up too much battery power.
    • Dr.sunil V
      June 19, 2014 at 3:14 pm

      Thanks. Though such tech details are beyond my understanding , please tell , which of the three most prevent battery heating : higher strength ( 1 GHZ , 2 GHZ ) or core number ( Dual , Quad , Octa ) or architecture ( 86 ) ?

    • Oron J
      June 19, 2014 at 6:39 pm

      Very very broadly, a dual or quad CPU with a lower speed is better (in terms of battery life anyway) than other combinations. However, it depends a lot on your use of the phone. There's not a single right answer (if there was, everybody would be making that phone!).

    • Drsunil V
      June 25, 2014 at 9:51 am

      Thanks. You mentioned about impact of core numbers on battery of android device. Please tell , what are other impacts of core numbers and also of processor strength ( 1 GHZ , 2 GHZ ) on the functionalities of android device ( battery , speed of interface , multitasking et al )

  3. Hovsep A
    June 17, 2014 at 5:30 pm

    the performance consists of processor speed and number of cores also virtual cores. the x86 architecture grants developers access to the largest collection of software. There are situations where the x86 processors are not the right choice of microprocessor. Arm chips can contain many many core system components: CPUs, GPUs and DSPs. A quad-core processor is faster than a dual-core processor only when it’s running an application that’s been developed to take advantage of its abilities.

    TEGRA K1—THE WORLD'S MOST ADVANCED MOBILE PROCESSOR -
    http://www.nvidia.com/object/tegra-k1-processor.html

    Nvidia Tegra K1 (32-bit) vs Qualcomm Snapdragon 805
    http://versus.com/en/nvidia-tegra-k1-32-bit-vs-qualcomm-snapdragon-805

    Top 5 quad-core Android smartphone processors
    http://www.techulator.com/resources/9712-Top-5-quad-core-Android-smartphone-processor.aspx

  4. Dr.sunil V
    June 17, 2014 at 5:11 pm

    TO rephrase the ques : How does core-number ( dual , quad , octa ) and strength ( 1 GHZ , 1.6 GHZ ) of process DIFFER in providing efficiency ( quickness , multi-tasking , lag time in transition from one interface to another )

    • Drsunil V
      June 25, 2014 at 11:32 am

      Checking

  5. Susendeep D
    June 17, 2014 at 4:20 pm

    Usually,the strength of core determines the good performance of a phone.Phone manufacturers make processors with highest performance only on their high end phones which have more number of cores than their mid to low end counterparts.
    If the stronger cores are more in number then performance will be good.If the strength of cores is less and they are more in number,then it'll deliver less or equal performance to that of former case i.e. 4 cores vs 8 cores.

    Also,important is the case that the OS and processor itself must work together to make all the number of cores with whatever strength it has to deliver performance.
    For instance,Exynos octa core 5410 didn't have support for HMP which was provided by 5420 but partially.There were speculations for providing a workaround to make all the 8 cores run simultaneously,but scrapped due to thermal issues.
    Apps must be designed to support all these number of cores to deliver that level of performance.

    • Dr.sunil V
      June 19, 2014 at 3:07 pm

      TO rephrase the ques : How does core-number ( dual , quad , octa ) and strength ( 1 GHZ , 1.6 GHZ ) of process DIFFER in providing efficiency ( quickness , multi-tasking , lag time in transition from one interface to another )

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