GPU Analysis/Performance

Section by Anand Shimpi

Understanding the A6's GPU architecture is a walk in the park compared to what we had to do to get a high level understanding of Swift. The die photos give us a clear indication of the number of GPU cores and the width of the memory interface, while the performance and timing of release fill in the rest of the blanks. Apple has not abandoned driving GPU performance on its smartphones and increased the GPU compute horsepower by 2x. Rather than double up GPU core count, Apple adds a third PowerVR SGX 543 core and runs the three at a higher frequency than in the A5. The result is roughly the same graphics horsepower as the four-core PowerVR SGX 543MP4 in Apple's A5X, but with a smaller die footprint.

As a recap, Imagination Technologies' PowerVR SGX543 GPU core features four USSE2 pipes. Each pipe has a 4-way vector ALU that can crank out 4 multiply-adds per clock, which works out to be 16 MADs per clock or 32 FLOPS. Imagination lets the customer stick multiple 543 cores together, which scales compute performance linearly.

SoC die size however dictates memory interface width, and it's clear that the A6 is significantly smaller in that department than the A5X, which is where we see the only tradeoff in GPU performance: the A6 maintains a 64-bit LPDDR2 interface compared to the 128-bit LPDDR2 interface in the A5X. The tradeoff makes sense given that the A5X has to drive 4.3x the number of pixels that the A6 has to drive in the iPhone 5. At high resolutions, GPU performance quickly becomes memory bandwidth bound. Fortunately for iPhone 5 users, the A6's 64-bit LPDDR2 interface is a good match for the comparatively low 1136 x 640 display resolution. The end result is 3D performance that looks a lot like the new iPad, but in a phone:

Mobile SoC GPU Comparison
  Adreno 225 PowerVR SGX 540 PowerVR SGX 543MP2 PowerVR SGX 543MP3 PowerVR SGX 543MP4 Mali-400 MP4 Tegra 3
SIMD Name - USSE USSE2 USSE2 USSE2 Core Core
# of SIMDs 8 4 8 12 16 4 + 1 12
MADs per SIMD 4 2 4 4 4 4 / 2 1
Total MADs 32 8 32 48 64 18 12
GFLOPS @ 200MHz 12.8 GFLOPS 3.2 GFLOPS 12.8 GFLOPS 19.2 GFLOPS 25.6 GFLOPS 7.2 GFLOPS 4.8 GFLOPS

We ran through the full GLBenchmark 2.5 suite to get a good idea of GPU performance. The results below are largely unchanged from our iPhone 5 Performance Preview, with the addition of the Motorola RAZR i and RAZR M. I also re-ran the iPad results on iOS 6, although I didn't see major changes there.

We'll start out with the raw theoretical numbers beginning with fill rate:

GLBenchmark 2.5 - Fill Test

The iPhone 5 nips at the heels of the 3rd generation iPad here, at 1.65GTexels/s. The performance advantage over the iPhone 4S is more than double, and even the Galaxy S 3 can't come close.

GLBenchmark 2.5 - Fill Test (Offscreen 1080p)

Triangle throughput is similarly strong:

GLBenchmark 2.5 - Triangle Texture Test

Take resolution into account and the iPhone 5 is actually faster than the new iPad, but normalize for resolution using GLBenchmark's offscreen mode and the A5X and A6 look identical:

GLBenchmark 2.5 - Triangle Texture Test (Offscreen 1080p)

The fragment lit texture test does very well on the iPhone 5, once again when you take into account the much lower resolution of the 5's display performance is significantly better than on the iPad:

GLBenchmark 2.5 - Triangle Texture Test - Fragment Lit

GLBenchmark 2.5 - Triangle Texture Test - Fragment Lit (Offscreen 1080p)

GLBenchmark 2.5 - Triangle Texture Test - Vertex Lit

GLBenchmark 2.5 - Triangle Texture Test - Vertex Lit (Offscreen 1080p)

The next set of results are the gameplay simulation tests, which attempt to give you an idea of what game performance based on Kishonti's engine would look like. These tests tend to be compute monsters, so they'll make a great stress test for the iPhone 5's new GPU:

GLBenchmark 2.5 - Egypt HD

Egypt HD was the great equalizer when we first met it, but the iPhone 5 does very well here. The biggest surprise however is just how well the Qualcomm Snapdragon S4 Pro with Adreno 320 GPU does by comparison. LG's Optimus G, a device Brian flew to Seoul, South Korea to benchmark, is hot on the heels of the new iPhone.

GLBenchmark 2.5 - Egypt HD (Offscreen 1080p)

When we run everything at 1080p the iPhone 5 looks a lot like the new iPad, and is about 2x the performance of the Galaxy S 3. Here, LG's Optimus G actually outperforms the iPhone 5! It looks like Qualcomm's Adreno 320 is quite competent in a phone. Note just how bad Intel's Atom Z2460 is, the PowerVR SGX 540 is simply unacceptable for a modern high-end SoC. I hope Intel's slow warming up to integrating fast GPUs on die doesn't plague its mobile SoC lineup for much longer.

GLBenchmark 2.5 - Egypt Classic

The Egypt classic tests are much lighter workloads and are likely a good indication of the type of performance you can expect from many games today available on the app store. At its native resolution, the iPhone 5 has no problems hitting the 60 fps vsync limit.

GLBenchmark 2.5 - Egypt Classic (Offscreen 1080p)

Remove vsync, render at 1080p and you see what the GPUs can really do. Here the iPhone 5 pulls ahead of the Adreno 320 based LG Optimus G and even slightly ahead of the new iPad.

Once again, looking at GLBenchmark's on-screen and offscreen Egypt tests we can get a good idea of how the iPhone 5 measures up to Apple's claims of 2x the GPU performance of the iPhone 4S:

Removing the clearly vsync limited result from the on-screen Egypt Classic test, the iPhone 5 performs about 2.26x the speed of the 4S. If we include that result in the average you're still looking at a 1.95x average. As we've seen in the past, these gains don't typically translate into dramatically higher frame rates in games, but games with better visual quality instead.

General Purpose Performance Increased Dynamic Range: Understanding the Power Profile of Modern SoCs
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  • dagamer34 - Tuesday, October 16, 2012 - link

    Yeah, when are we going to see PowerVR 6? Reply
  • ltcommanderdata - Tuesday, October 16, 2012 - link

    I think it's expected mid-2013, so it would have been a big stretch to have made it for the iPhone 5. Apple didn't really have that much choice with sticking to the SGX543MP since happened to be off cadence. Even making it for the iPad 4 might be iffy. Reply
  • peat - Tuesday, October 16, 2012 - link

    I was pushed to see the 'considerable' difference between the thickness of the iP4 and iP5 in the pic. Looking at the dimensions in the table it's thinner by a truly staggering 11%.

    Q. Since when has an 11% change in anything equated to "considerable". But yup, I still want one.
    Reply
  • darwinosx - Tuesday, October 16, 2012 - link

    To anyone who knows anything about smartphone design and what goes into the device. Reply
  • Alucard291 - Tuesday, October 16, 2012 - link

    No offence but to a consumer that's still 11%. I.e. not even 1/5 reduction.

    What I'm trying to get at here is that its negligible to most users and touting it as an improvement is only marketing blurb.
    Reply
  • Sufo - Tuesday, October 16, 2012 - link

    IRL i've noticed the reduction, you'd be surprised how good your hands are at picking up (forgive the pun) on these things. Still, it's not a huge change, admittedly, and it was almost mandatory with the increase in height. Nevertheless once again a nice device to hold. Reply
  • doobydoo - Friday, October 19, 2012 - link

    Exactly.

    If you actually try holding an iPhone 5 you'll immediately notice how obvious it is that it's significantly thinner and lighter.

    And as someone else said - it's 18% thinner, not 11.
    Reply
  • Kidster3001 - Monday, October 22, 2012 - link

    really dooby?

    From someone who has always said 4" was way to big and 3.5" was perfect? Now you like 4" displays?
    Reply
  • Aenean144 - Tuesday, October 16, 2012 - link

    Since when does (1 - 7.6/9.3) = 11%?

    My calculator says the iPhone 5 is 18% thinner than the iPhone 4.
    Reply
  • edsib1 - Tuesday, October 16, 2012 - link

    Your android benchmarks are meaningless if you dont use a) best browser and b) latest drivers. Phones with later version drivers will have higher scores.

    HTC One X (Tegra3) - official RUU 4.04 & Chrome

    Kraken - 21095
    Google V8 - 1578
    Octane V1 - 1684
    Sunspider - 1172
    Browsermark - 130288

    HTC One X (Tegra3) - Eternity Kernel (3.4) & Chrome

    Kraken - 18750
    Google V8 - 1791
    Octane V1 - 1922
    Sunspider - 1084
    Browsermark - 162580
    Reply

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