GPU Performance

Since the iPad Air uses the same A7 silicon as the iPhone 5s, it also uses the same on-die GPU as the 5s: IMG’s PowerVR G6430. This is a 4-cluster configuration of IMG’s latest graphics hardware, running at some relatively high frequency. I already went into some detail on the G6430 in our 5s review so I won’t rehash that here, but we’re basically looking at a shift to a more efficient scalar architecture.

I still don’t have confirmations of clock speeds, but I believe we’re looking at a max GPU clock of around 450MHz. As you’ll see from the results below, there’s a small difference in performance between the iPad Air and iPhone 5s in terms of peak GPU performance - implying very similar clocks. The difference is the iPad Air should be able to sustain its max frequency longer than the iPhone 5s can.

Mobile SoC GPU Comparison
  PowerVR SGX 554MP4 PowerVR G6430 PowerVR G6430
Used In iPad 4 iPhone 5s iPad Air
SIMD Name USSE2 USC USC
# of SIMDs 32 4 4
MADs per SIMD 4 32 32
Total MADs 128 128 128
GFLOPS @ 300MHz 76.8 GFLOPS 76.8 GFLOPS 76.8 GFLOPS
GFLOPS as Shipping 68.1 GFLOPS (?) 115.2 GFLOPS 115.2 GFLOPS

Since we’re talking about an A7 here and not an X-series SoC, there’s still only a 64-bit wide memory interface. As memory bandwidth is a key enabler of GPU performance I was curious to see how GPU performance compared to the outgoing iPad 4 with its much wider memory interface. Do keep in mind that the A7 does include a large system cache on-die, which can help improve effective memory bandwidth.

GFXBench 2.7

We'll start our GPU performance analysis with a look at low level results using GFXBench/GLBenchmark 2.7. The low level tests, particularly the offscreen ones, should give us some idea as to whether or not there's any increase in GPU frequency for the iPad Air vs. iPhone 5s implementations of A7.

GLBenchmark 2.7 - Fill Test (Onscreen)

GLBenchmark 2.7 - Fill Test (Offscreen)

Looking at the fill rate results, there's a 4.5% increase in performance compared to the iPhone 5s. That could be the magnitude of clock increase that we're seeing between A7s. Apple could very well be relying on more thermal headroom in the iPad Air to provide any real world GPU performance advantages over the iPhone 5s.

GLBenchmark 2.7 - Triangle Throughput (Onscreen)

GLBenchmark 2.7 - Triangle Throughput (Offscreen)

We see an even smaller gap between the Air and 5s in the triangle throughput tests (2.9%). There doesn't seem to be any substantial difference in GPU frequency between A7 implementations here. The regression in triangle rate performance compared to the iPad 4 is explained by differences in how Series 6 and Series 5XT GPUs scale in width. Whereas 5XT replicated nearly the entire GPU for "multi-core" versions, multi-cluster versions of Rogue only replicate at the shader array. The result? We don't see the same sort of peak triangle setup scaling we did back on multi-core 5XT parts. I'm not sure I'm particularly happy with the magnitude of the regression here, but I haven't seen any real world cases where it matters yet.

Next up are the game simulation tests. We'll start with the more strenuous of the two: T-Rex HD.

GLBenchmark 2.7 - T-Rex HD (Onscreen)

Here we get closer to Apple's claims of a 2x increase in performance. The iPad Air delivers 75% more performance than the iPad 4 in this test. Once again the iPhone 5s pulls ahead but that's because the onscreen tests render at display resolution, which is lower on the 5s.

GLBenchmark 2.7 - T-Rex HD (Offscreen)

Offscreen performance sees similar scaling: ~69% better performance compared to the iPad 4.

GLBenchmark 2.5 - Egypt HD (Onscreen)

GLBenchmark 2.5 - Egypt HD (Offscreen)

3DMark

We're once again running 3DMark's newest Unlimited mode which does its best to run independently of v-sync and at a standard resolution across all devices. I've also included 3DMark Extreme results below that feature a few more comparison points.

3DMark Unlimited - Ice Storm

The overall Ice Storm scores show a 36% improvement in performance over the iPad 4 and an 8% increase compared to the iPhone 5s. Given the CPU frequency advantage of the A7 in the Air vs. the iPhone 5s, I'm guessing that's why we're seeing the performance gap we are here.

3DMark Unlimited - Graphics Score

If we focus exclusively on the GPU tests (which themselves are still CPU bound), the iPad Air's performance advantage over the iPad 4 grows to over 60%.

3DMark Unlimited - Graphics Test 1

3DMark Unlimited - Graphics Test 2

3DMark Unlimited - Physics Score

I'm still not entirely sure what's going on with the 3DMark Physics test, but we've seen this two reviews in a row now where Cyclone showed no performance increase at all compared to Swift despite this being largely a CPU test.

3DMark - Ice Storm (Extreme)

3DMark - Graphics Score (Extreme)

3DMark - Graphics Test 1 (Extreme)

3DMark - Graphics Test 2 (Extreme)

3DMark - Physics Score (Extreme)

Basemark X

Basemark X is a new addition to our mobile GPU benchmark suite. There are no low level tests here, just some game simulation tests run at both onscreen (device resolution) and offscreen (1080p, no vsync) settings. The scene complexity is far closer to GLBenchmark 2.7 than the new 3DMark Ice Storm benchmark, so frame rates are pretty low.

I'm still having random issues with Basemark X reliably running both on and offscreen tests on iOS 7. Unfortunately I could only get onscreen results for the iPad Air, which came in at 46% faster than the iPad 4. Note the iPad mini and iPhone 5s benefit from having lower native resolutions here, which is why they perform so well.

Basemark X (Onscreen)

CPU Changes, Performance & Power Consumption Display
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  • over9k - Tuesday, October 29, 2013 - link

    Remember, Mavericks' big focus is RAM management. There's no reason to think iOS 7 also doesn't do some great RAM management. It's just that when talking mobile, that's not the "it" talk. Also, it's important to note that iOS devices have always used lower amounts of memory - they are just very well optimized.
  • tipoo - Tuesday, October 29, 2013 - link

    Mavericks borrowed how iOS already used memory, with background apps being able to be pushed out of memory if need be. iOS7 isn't getting Mavericks memory management, Mavericks is just getting the management iOS already had since its inception.
  • kirsch - Tuesday, October 29, 2013 - link

    I think over9k is referring to memory compression introduced in Mavericks. As far as I know this was never in iOS.
  • tipoo - Tuesday, October 29, 2013 - link

    The compression seems to work on idle apps too though, and iOS would run only one foreground app with most of the memory available to it. I just don't think it will help as much on a mostly single tasking OS.
  • NetMage - Wednesday, October 30, 2013 - link

    Actually it should help more as the recent Apps on iOS are mostly don't to run at all, but are kept in memory to improve swapping speed - these could be easily compressed with no impact on user experience.
  • tipoo - Wednesday, October 30, 2013 - link

    People saying Mavericks like compression will help: Anand measured how much RAM was in use under load. If it was compressing something, it would have been factored into how much was used. This is no holy grail here.
  • darwinosx - Wednesday, October 30, 2013 - link

    You think it needs 2 GB of ram why? It obviously doesn't. This isn't Windows or Android.
  • DarkXale - Wednesday, October 30, 2013 - link

    Because Safari is famous for resetting tabs (lost work), and many iOS apps are notorious for dropping undo states the very second you switch out of them. (Which you have to due to the inability to display more than one app at a time)

    Both cause data loss, which is one of the most serious events that can occur in computer systems.

    Both are due to RAM constraints.
  • dugbug - Wednesday, October 30, 2013 - link

    I have not seen that in ios7, they rewrote that behavior significantly. Would it benefit from more ram? sure. Or they could just rewrite it to cache tabs better.
  • tipoo - Wednesday, October 30, 2013 - link

    Because even with 30% less RAM use on 32 bit iOS, Safari boots tabs out like crazy and has to reload a lot of apps from NAND when switching.

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