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 ?

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?


View All Comments

  • Davabled - Monday, October 31, 2011 - link

    With Field test enabled, do numbers closer to zero indicate a better connection? (I'm referring to the numbers that replace the bars in the upper left corner) Reply
  • Anand Lal Shimpi - Monday, October 31, 2011 - link

    Correct :)

    Take care,
  • Formul - Monday, October 31, 2011 - link

    why the huge drop from iPad 2 to iPhone 4S in the GL benchmark pro? its only about 30% performance .... any explanation? Reply
  • Anand Lal Shimpi - Monday, October 31, 2011 - link

    Because the number was incorrect :-P Fixed now :)

    Take care,
  • ZebuluniteX - Monday, October 31, 2011 - link

    Great review as always Anand!

    In addition to the GL benchmark pro results Formul mentioned, I was also surprised to see the Motorola Droid RAZR for some reason do far better than other Gingerbread-based Android smartphones. It is listed as using different version of Android (2.3.5 vs 2.3.4 or older), but given that very similar results were shown between the iPhone 4S and Honeycomb-running Galaxy Tab 8.9 in your 'iPhone 4S Preliminary Benchmarks' article (where the 4S was a bit slower than the Galaxy Tab in SunSpider, and marginally faster in BrowserMark), I'm guess those are just mislabeled Galaxy Tab results. Is that the case?
  • Anand Lal Shimpi - Monday, October 31, 2011 - link

    Thank you - be sure to thank Brian Klug as well, he really did the bulk of the heavy lifting here. I just popped in to talk about silicon and battery life.

    The RAZR numbers are what we ran at the RAZR announcement:

    The improvement is likely due to an updated browser from Motorola. I included those numbers effectively as a placeholder until Ice Cream Sandwich arrives :)

    Take care,
  • ZebuluniteX - Tuesday, November 01, 2011 - link

    Ah, thanks for the clarification, I missed that article. Hmm, that's interesting that, apparently, Motorola "ported" Honeycomb or Ice Cream Sandwich's browser optimizations to Gingerbread (or at least I assume that's what happened)...

    I'm in the market for a smartphone, and while I was leaning towards the 4S since I already am in the Apple ecosystem via an iPod Touch 2G, before pulling the trigger I wanted to read the Anandtech take on it. The review was excellent as always - thanks again to both you and Brian!
  • Formul - Monday, October 31, 2011 - link

    that was fast! i knew something was not right as there was no mention of this in the text :-)

    thanks for another great review, keep up the good work! :-)
  • zanon - Monday, October 31, 2011 - link

    The article wrote "The expectation that Apple will always deliver more than just a hardware upgrade is likely what made Siri a 4S exclusive."
    While only time will tell for sure, it seems quite possible that graduated ramp up had a bigger role to play here. As you say, most of the heavy duty lifting for Siri is going on server-side, and in turn local processing needs aren't too bad. However, the natural flip side of that of course is that the server-side infrastructure is required for the service to work at all, and resources aren't unlimited there either. Even with it limited purely to 4S users, Siri still had some availability problems in the first few days as millions activated and tried to user it simultaneously. It's not hard to imagine what would have happened if every single one of the tens of millions able to upgrade to iOS 5 *also* tried to start using it immediately. Apple has built a huge data center and that's all well and good, but nothing substitutes for actual working experience when it comes to massive software services.

    By limiting the initial rollout, Apple can do performance profiling, get an idea of average loads after initial "let's try it" dies down, and so forth. Staggering a rollout also means being able to plan for the general load rather then suffering the classic and well known double-bind of
    A) Building for a peak load, and ending up being left with a lot of extraneous hardware that barely gets used.
    B) Building for the average, then suffering from embarrassing and headline generating outages for a week or two.

    It's true they could just decide to keep it 4S only, but given they are still selling the iPhone 4, and probably make plenty of profit on that now very mature device, I think there is a decent chance they'll roll it out to a wider audience down the road.

    Also, a few typos:
    Page 2:
    I think the phrase is "pretty much par for the *course* for Apple..." rather then "par for the case".

    Pg 9, WiFi:
    "...newest WLAN, Bluetooth, and FM *cobo* chip" should I think be "combo".

    Pg 15:
    ...4S, without a (big blank, presumably some sentence was supposed to go here?)

    Pg 16:
    "aren't simply *academical*" should be "academic".

    Again, great review, thank you.
  • Anand Lal Shimpi - Monday, October 31, 2011 - link

    That's a very good point, I will add it to the discussion. The sinister view is to assume Apple did it to differentiate, the balanced view takes into account infrastructure, which is exactly what you did here :)

    And thanks for the corrections :)

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