The Mali-400

Now that we've settled the issue of what type of GPU it is, let's talk about the physical makeup of the Mali-400. The Mali-400 isn't a unified shader architecture, it has discrete execution hardware for vertex and fragment (pixel) processing. ARM calls the Mali-400 a multicore GPU with configurations available with 1 - 4 cores. When ARM refers to a core however it's talking about a fragment (pixel shader) processor, not an entire GPU core. This is somewhat similar to NVIDIA's approach with Tegra 2, although NVIDIA counts each vertex and fragment processor as an individual core.

In its simplest configuration the Mali-400 features a single combined geometry front end and vertex processor and a single fragment processor. The 400 is also available in 2 and 4 core versions, both of which still have only a single vertex processor. The two core version has two fragment processors and the four core version has four fragment processors. Note that ARM decided to scale fragment shading performance with core count while keeping vertex performance static. This is likely the best decision given current workloads, but a risky one. NVIDIA on the other hand standardized on a 1:1 ratio between fragment and vertex processors compared to ARM's 4:1 on a 4-core Mali-400. The 4-core Mali-400 MP4 is what Samsung uses in the Exynos 4210.

ARM, like Qualcomm, isn't particularly interested in having the details of its GPUs available publicly. Unfortunately this means that we know very little about the makeup of each of these vertex and fragment processors. I suspect that both companies will eventually learn to share (just as AMD and NVIDIA did) but as this industry is still in its infancy, it will take some time.

Earlier documentation on Mali revealed that the GPU is a VLIW architecture, meaning each processor is actually a collection of multiple parallel execution units capable of working on vector data. There's no public documentation indicating how wide each processor is unfortunately, but we can make some educated guesses.

We know from history that AMD felt a 5-wide VLIW architecture made sense for DX9 class games, later moving down to a 4-wide architecture for DX11 games. AMD didn't have the die constraints that ARM and other SoC GPU suppliers do so a 5-wide unit is likely out of the question, especially considering that Imagination settled on a VLIW4 architecture. Furthermore pixels have four color elements (RGBA), making a VLIW4 an ideal choice.

Based on this as well as some internal information we can assume that a single Mali fragment shader is a 4-wide VLIW processor. The vertex shader is a big unknown as well, but knowing that vertex processing happens on two coordinate elements (U & V) Mali's vertex shader is likely a 2-wide unit.

Thus far every architecture we've looked at has been able to process one FP16 MAD (multiply+add) per execution unit per clock. If we make another assumption about the Mali-400 and say it can do the same, we get the following table:

Mobile SoC GPU Comparison
  PowerVR SGX 535 PowerVR SGX 540 PowerVR SGX 543 PowerVR SGX 543MP2 Mali-400 MP4 GeForce ULP Kal-El GeForce
SIMD Name USSE USSE USSE2 USSE2 Core Core Core
# of SIMDs 2 4 4 8 4 + 1 8 12
MADs per SIMD 2 2 4 4 4 / 2 1 ?
Total MADs 4 8 16 32 18 8 ?
GFLOPS @ 200MHz 1.6 GFLOPS 3.2 GFLOPS 6.4 GFLOPS 12.8 GFLOPS 7.2 GFLOPS 3.2 GFLOPS ?
GFLOPS @ 300MHz 2.4 GFLOPS 4.8 GFLOPS 9.6 GFLOPS 19.2 GFLOPS 10.8 GFLOPS 4.8 GFLOPS ?

Based on this estimated data alone, it would appear that a four-core Mali-400 has the shader compute power of a PowerVR SGX 543. In other words, half the compute horsepower of the iPad 2's GPU or over twice the compute of any smartphone GPU today. The Mali-400 is targeted at 275MHz operation, so its figures are likely even higher than the competition. Although MADs are quite common in shader execution, they aren't the end all be all - we need to look at application performance to really see how it stacks up.

Understanding Rendering Techniques GPU Performance: Staggering
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  • ph0tek - Sunday, September 11, 2011 - link

    First of all Android is better than iOS in so many ways that i'd be here all day listing them..... and the same goes for this phones hardware compared to the iPhone so i wont even bother!

    Secondly the S2 might have a slightly lower display res but it has better response times, infinitely better contrast, vastly better blacks, more vibrant colours, plus superior viewing angles. And all this on a screen that isn't stupidly tiny. It's clearly better overall.
    Everyone who i've shown to this phone to instantly says the screen is the best they've seen, even iPhone users.

    With the battery theres not much difference, it has longer battery life for talk time than iPhone, and also longer battery when using hotspots, while displaying Flash content too! Yes you can view the WHOLE web on this.

    I find it very amusing that you even try to compare the iPhone to this. Theres simply no comparison. Like comparing a ferrari to a skoda. Just makes you look stupid.
    Reply
  • niva - Monday, September 12, 2011 - link

    Why are you arguing with an iFanboy? Reply
  • LostViking - Saturday, September 17, 2011 - link

    You could argue that the SGS 2 is better (for me it wins hands down), and you could argue that the iPhone 4 is better.

    Some people get sever rashes all over their body by using products not made by Apple ;)
    For those people the original iPhone beats the SGS 2 and all future Android devices easily :)
    Reply
  • jjj - Sunday, September 11, 2011 - link

    hard to like any new phone now when Krait and A15 are around the corner. Reply
  • killerroach - Sunday, September 11, 2011 - link

    Remember... there's ALWAYS something around the corner. Reply
  • jjj - Monday, September 12, 2011 - link

    Actually there is rarely something like this around the corner.This time we got both new cores and a new node (and the jump from 40/45 nm to 28 nm is pretty big). Reply
  • 3lackdeath - Sunday, September 11, 2011 - link

    Nice phone but WP7 is faster and smoother. Reply
  • OBLAMA2009 - Sunday, September 11, 2011 - link

    400x800? no thx Reply
  • MacTheSpoon - Sunday, September 11, 2011 - link

    What a staggeringly awesome review. I am really impressed. The audio section--wow.

    I sure wish the screen were brighter and the audio better on this phone, but I have to put it on my short list.
    Reply
  • Piyono - Sunday, September 11, 2011 - link

    "There, Anand and *I* played with..." Reply

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