GPU Performance Using Unreal Engine 3

In our iPad 2 review I called the PowerVR SGX 543MP2 Apple's gift to game developers. Apple boasted a roughly 9x improvement in raw GPU compute power over the A4 into the A5. The increase came through more execution resources and a higher GPU clock. The A5 in the iPhone 4S gets the same GPU, simply clocked lower than the iPad 2 version. Apple claims the iPhone 4S can deliver up to 7x the GPU performance of the iPhone 4, down from 9x in the iPad 2 vs. iPad 1 comparison. Why the delta?

The iPad 2 has both a larger battery and a higher resolution display. There are 28% more pixels to deal with on the iPad 2 vs the iPhone 4S and 9x vs 7x actually works out to be a 28% increase. The lower clocked GPU goes along with the lower clocked CPU in the 4S' version of the A5 to keep power consumption in check and because the platform doesn't need the performance as much as the iPad 2 with its higher resolution display.

Mobile SoC GPU Comparison
  Adreno 225 PowerVR SGX 540 PowerVR SGX 543 PowerVR SGX 543MP2 Mali-400 MP4 GeForce ULP Kal-El GeForce
SIMD Name - USSE USSE2 USSE2 Core Core Core
# of SIMDs 8 4 4 8 4 + 1 8 12
MADs per SIMD 4 2 4 4 4 / 2 1 ?
Total MADs 32 8 16 32 18 8 ?
GFLOPS @ 200MHz 12.8 GFLOPS 3.2 GFLOPS 6.4 GFLOPS 12.8 GFLOPS 7.2 GFLOPS 3.2 GFLOPS ?
GFLOPS @ 300MHz 19.2  GFLOPS 4.8 GFLOPS 9.6 GFLOPS 19.2 GFLOPS 10.8 GFLOPS 4.8 GFLOPS ?

GLBenchmark continues to be our go-to guy for GPU performance under iOS. While there are other reputable 3D benchmarks, GLBench remains the only good cross-platform (iOS and Android) solution we have today.

The performance gains live up to Apple's expectations (Update: our original 4S for Egypt/Pro were incorrect. We had two sets of graphs, one internal and one external - the latter had incorrect data. We have since updated the charts to reflect the 4S' actual performance. Sorry for the mixup!):

GLBenchmark 2.1 - Egypt - Offscreen

GLBenchmark 2.1 - Pro - Offscreen

GLBenchmark gets around vsync by rendering offscreen, so the 4S is allowed to run as fast as it can. Here we see a 6.46x higher frame rate compared to the iPhone 4.

It's obvious that GLBenchmark is designed first and foremost to be bound by shader performance rather than memory bandwidth, otherwise all of these performance increases would be capped at 2x since that's the improvement in memory bandwidth from the 4 to the 4S. Note that we're clearly not overly bound by memory bandwidth in these tests if we scale pixel count by 50%, which is hardly realistic. Most games won't be shader bound, instead they should be more limited by memory bandwidth.

At the iPhone 4S introduction Epic was on stage showing off Infinity Blade 2, which will have new visual enhancements only present on the 4S thanks to its faster GPU. Thus far Epic has been using GPU performance improvements to make its games look better and not necessarily run faster (although they do) since the target is playability on all platforms. What I wanted however was a true apples-to-apples comparison using Epic's engine as it is arguably the best looking platform to develop iOS games on today.

Epic offers a free license to Unreal Engine 3 to anyone who wants to use it for non-commercial use. If you want to sell your UE3 based iOS game, you don't have to pay a large sum to license Epic's engine up front. Instead you toss Epic $99 and pay royalties (25%) on any revenue beyond the first $50K. It's a great deal for aspiring game developers since you get access to one of the best 3D engines around and don't need any additional startup capital to use it. If your game is a hit Epic gets a cut but you're still making money so all is good in the world.

The process starts with UDK, the Unreal Development Kit. Epic actually offers a great deal of documentation on developing using UDK, making the whole process extremely easy. The freely available UDK can target Windows, Mac OS X and iOS platforms. If you want Android support you'll have to pay to license the dev kit unfortunately. Given how successful Infinity Blade has been under iOS, I suspect this is a move partially designed to keep Apple happy. It's also possible the Android UE3 dev kit is simply not as far along as the iOS version.

Along with every UDK download, Epic now provides the full source code to its well known iOS Citadel demo. With access to Citadel's source code and Epic's excellent (and freely available) development tools I put together a real-world GPU test for iOS.


What's that? A frame counter in iOS? Huzzah!

The test shows us frame rate over the course of a flythrough of Epic's Citadel demo. This is simply the standard Citadel guided tour but with UE3's frame recording statistics enabled. Once again, UDK gave me the tools needed to accurately profile what was going on. For developers this would be helpful in tuning the performance of your app, but for me it gave me the one thing I've been hoping for: average frame rate in a UE3 game for iOS.

The raw data looks like this, a graph of frame render times:


iPhone 4S frame time

You're looking at frame render time in ms, so lower numbers mean better performance. Notice how the iPhone 4S graph seems to remain mostly flat for the majority of the benchmark run? That's because it's limited by vsync. At 60Hz the frame render time is capped to 16.7ms, which is approximately where the 4S' curve flattens out to. The 4S could likely run through this demo even quicker (or maintain the same speed with a heavier graphical workload) if we had a way to disable vsync in iOS.


iPhone 4 frame time

On the iPhone 4 however, frame times are significantly higher - more than 2x on average. You also see significant spikes in frame time, indicating periods where the frame rate drops significantly. Not only does the 4S offer better average performance here but its performance is far more consistent, hugging vsync rather than wildly bouncing around.

The chart below summarizes the two graphs above by looking at the average frames rendered per second throughout the benchmark:

AnandTech UE3 Performance Test

The iPhone 4S averages 2.3x the frame rate of the iPhone 4 throughout our test. I believe this gives us a more realistic value than the 6x we saw in GLBenchmark. A major cause for the difference is the vsync limitations present in all iOS apps that render to the screen. On top of that, while we're obviously not completely limited by memory bandwidth, it's clear that memory bandwidth does play a larger role here than it does in GLBenchmark.

The Citadel demo by default increases rendering quality on the iPhone 4, but a quick look at the game's configuration files didn't show any new features enabled for the 4S. Chances are the version of Citadel included with the UDK was built prior to the 4S being available. In other words, the 4 and 4S should be rendering the same workload in our benchmark. To confirm I also grabbed a couple of screenshots to ensure the two devices were running at the same settings:


iPhone 4


iPhone 4S

This is actually the most stressful scene in the level, it causes even the 4S to drop below 30 fps. With the camera stationary in roughly the same position I saw a 74% increase in performance on the 4S vs the iPhone 4.

Most game developers still target the iPhone 3GS, but the 4S allows them to significantly ramp up image quality without any performance penalty. Because of the lower hardware target for most iOS games and forced vsync I wouldn't expect to see 2x increases in frame rate for the 4S over the 4 in most games out today or in the near future. You can expect a smoother frame rate and better looking games if developers follow Epic's lead and simply enable more eye-candy on the 4S.

The Memory Interface The A6: What's Next?
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  • freezer - Thursday, November 03, 2011 - link

    I think you should have the GPU benchmark using phone's native resolution. That would give more accurate results in real world gaming situation than running all phones using same resolution.

    The iPhone 4S 3.5" screen has much more pixels than Galaxy S2 4.3" screen which gives latter advantage in 3D speed. That is because the GPU has to draw every pixel in every frame. There's no way around it.

    In fact running GL Benchmark 2.1 Pro High in native resolution gives very different results as Galaxy S2 comes at top:

    http://glbenchmark.com/result.jsp?benchmark=glpro2...
    Reply
  • thunng8 - Thursday, November 03, 2011 - link

    You do realize that the top 3 results are all vsync limited? They are all close to 60fps. That makes it not a great test to show the full potential of the gpu. Reply
  • ReverendDC - Friday, November 04, 2011 - link

    I was wondering why there were no WPs in your comparison. They have comparable screens, functionality, and features.

    This is NOT to start a flame war. I am curious about how some of the newer WPs especially line up (Titan, Lumina 800, Focus S, etc).

    Thanks!
    Reply
  • mymomentummedia - Sunday, November 06, 2011 - link

    Here is a 360 degreee review of the iPhone 4s with a beautiful girl in a swimsuit... no complaints here.

    http://www.youtube.com/watch?v=-eNxXBIV9_s
    Reply
  • yeatzeck - Sunday, November 06, 2011 - link

    According to the Chipworks (http://www.chipworks.com/en/technical-competitive-... in iPhone 4S is Sony's camera (they even X-ray it).
    You probably have to update the review.
    Reply
  • mosmov - Monday, November 07, 2011 - link

    You've run the Taiji for many devices so far.
    I'd like to see the number also for 4S to align the result with other devices in my memory.
    Reply
  • tipoo - Monday, January 02, 2012 - link

    Taiji is for Android... Reply
  • Conficio - Monday, November 07, 2011 - link

    Text dictation is a neat feature for sure, but to be honest I’m still not likely to rely on it for sending or replying to messages. It’s convenient while driving but the accuracy isn’t high enough to trust it with sending messages to important contacts.


    Here is the viral tip for Apple (or its competitors). Make it an option to deliver the text as well as the ability for the recipient to actually listen to the voice command recorded (sans the edit commands, etc.) That will become fast the fastest way to leave voice messages, because you don't have to wait for the phone to dial, time out and get through the voice mail instructions.
    Reply
  • HelloChris - Monday, November 07, 2011 - link

    Long time reader, but something in this review made me register a username so I could add to the comments...

    Anand's webpage-refreshing battery life test saw the iPhone 4S achieve around 10 and 11 hours, for 3G and WiFi, respectively. However, MANY new 4S owners (including myself) have been getting battery life which is roughly half of that. I just finished reading this whole review, and I have to wonder if the test unit sent to Anandtech might have been hand-picked by Apple? 10/11 hours is just so much more than everyone else seems to be getting. I've averaged 6.5 hours of total usage, and this includes several hours of use where I'm using absolutely no 3G/WiFi data, and minimal processing power (example: viewing a PDF, viewing pictures, reading items on my Google Reader feed)...

    If you look on the major apple forums there are multiple threads where there are many users experiencing the same conditions.

    Also, I'm aware of the battery issue with iOS 5 (which Apple acknowledged last week and has a beta update out already for) which implies that this is indeed a software, not a hardware issue.

    Perhaps I'm missing something, but if it's the case that AnandTech received a well-performing test unit, that would explain their extraordinary battery life.
    Reply
  • doobydoo - Friday, December 02, 2011 - link

    I think you answer your own question.

    It sounds like your phone is affected by the battery life issue for which a software patch has been released, wheras Anand's probably wasn't.

    The vast majority of iPhone 4S owners didn't experience any issues with battery life.
    Reply

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