Phones/Tablets: Bandwidth Matters

GizmoChina has a very clear post explaining what I tried to do here and here and here: Why is eight-core (octa-core) still slow on cell phones?

Memory bandwidth is actually more crucial.

Smart phones and tablets are all SOC, meaning the graphics core is integrated, sharing memory bandwidth with the CPU, with no independent memory. And resolution is getting better for phones and tablets, this puts a great demand on memory bandwidth.

Programs need to run inside the internal memory. If the processor is quick, and the memory access speed can not keep up, the system will still be slow. And as resolution increases, so will the demand on memory bandwidth.

When memory bandwidth is not enough and resolution is too high, no matter how fast the processor is the system will still be slow.

See the entire post — and bookmark it for future reference.


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3 responses to “Phones/Tablets: Bandwidth Matters

  1. Very interesting articles! I have started to calculate the memory bandwidth on the Intel Z3735D is it seems rather insufficient taking in consideration the “Ipad target” which is around 4.0G/s per 1m pixels.
    Only the new snapdragon 801 and the 800 would be up to the perfect smooth ideal score… Including Tegra 4 and TEgra K1. Am i right?
    Which leaves me thinkng that chinese tablets are not yet “there”!

    • mikecane

      The only person who includes bandwidth in his write-ups is iambillbil. I don’t know how to go about calculating it — and am terrible at math, besides — so leave it up to the adepts to handle that.

      EDITED at add: No one at XDA has yet complained about the M802-based Onda V975M, so I think the tablets are getting better. Here’s iambillbil’s write-up about that tablet:
      If you scroll down far enough, he goes into bandwidth:

      Memory conditions in the control group

      Onda 975m +2048, effective memory 1455m, 799m users can boot occupied 655m, memory bandwidth 9.6g

      A 7039 +2048, effective memory 2006m, 888m users can boot occupied 1122m, memory bandwidth 9.6g
      A 4412 +2048, effective memory 1610m, 720m users can boot occupied 888m, memory bandwidth 6.4g
      A a31 +2048, effective memory 1596m, 755m users can boot occupied 841m, memory bandwidth 5.2g
      A 3188 +2048, effective memory 2048m, 788m users can boot occupied 1260m, memory bandwidth 4.9g
      A 5410 +2048, effective memory 1750m, 660m users can boot occupied 1017m, memory bandwidth 12.8g

  2. Thanks! From what understood from all the articles i found, the memory bandwidth is a crucial parameter to ensure overall smoothness.
    Let’s say the 4.0G/s minimum per 1,000,000 pixels – the iPad magic formula for retina displays. Formula: (“memory bandwidth of the system” X 1000 000) / (number of pixels) = ratio 4> good 4< bad.
    Xperia Tablet Z2- 2.304.000 pixels
    Snapdragon 801 memory bandwidth – 14.9G/s

    Total: 6.4G/s per 1 000 000 pixels – it's a perfect score

    Xperia Tablet Z- 2.304.000 pixels
    Snapdragon S4 Pro (APQ8064) memory bandwidth – 8.3G/s

    Total: 3.6G/s per 1 000 000 pixels – Lower than 4, which means that you might feel some performance issues, even though the cpu is powerful.

    Chinese tablets are still under the 4, most of them

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