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| iPad 4 GPU Performance Analyzed: PowerVR SGX 554MP4 Under the Hood Posted: 02 Nov 2012 10:46 AM PDT
As always, our good friends over at Kishonti managed to have the first GPU performance results for the new 4th generation iPad. Although the new iPad retains its 2048 x 1536 "retina" display, Apple claims a 2x improvement in GPU performance through the A6X SoC. The previous generation chip, the A5X, had two ARM Cortex A9 cores running at 1GHz paired with four PowerVR SGX 543 cores running at 250MHz. The entire SoC integrated 4 x 32-bit LPDDR2 memory controllers, giving the A5X the widest memory interface on a shipping mobile SoC in the market at the time of launch. The A6X retains the 128-bit wide memory interface of the A5X (and it keeps the memory controller interface adjacent to the GPU cores and not the CPU cores as is the case in the A5/A6). It also integrates two of Apple's new Swift cores running at up to 1.4GHz (a slight increase from the 1.3GHz cores in the iPhone 5's A6). The big news today is what happens on the GPU side. A quick look at the GLBenchmark results for the new iPad 4 tells us all we need to know. The A6X moves to a newer GPU core: the PowerVR SGX 554.
As always, Imagination doesn't provide a ton of public information about the 554 but based on what I've seen internally it looks like the main difference between it and the 543 is a doubling of the ALU count per core (8 Vec4 ALUs per core vs. 4 Vec4). Chipworks' analysis of the GPU cores helps support this: "Each GPU core is sub-divided into 9 sub-cores (2 sets of 4 identical sub-cores plus a central core)." I believe what we're looking at is the 8 Vec4 SIMDs. The 9th "core" is likely the extra ALU that all of the modern PowerVR GPUs have. We typically don't count it in the spec tables as I'm not really clear as to what its role is, but there's more theoretical compute power than what we list here. Based on the die shot and Apple's performance claims it looks like there are four PowerVR SGX554 cores on-die, resulting in peak theoretical performance greater than 77 GFLOPS. With that out of the way, let's get to the early performance results. We'll start with low level fill rate and triangle throughput numbers: Fill rate goes up by around 15% compared to the iPad, which isn't enough to indicate a huge increase in the number of texture units on the 554MP4 vs. the 543MP4. What we may be seeing here instead are benefits from higher clocked GPU cores rather than more texture units. If this is indeed the case it would indicate that the 554MP4 changes the texture to ALU ratio from what it was in the PowerVR SGX 543. The data here points to a GPU clock at least 15% higher than the ~250MHz in the 3rd generation iPad. Triangle throughput goes up by a hefty 65%, these are huge gains over the previous generation iPad. The fragment lit triangle test starts showing us close to a doubling of performance at the iPad's native resolution. Throw in a more ALU heavy workload and we really start to see the advantage of the new GPU: almost double the performance in Egypt HD at 2048 x 1536. We also get performance that's well above 30 fps here on the iPad at native resolution for the first time. Normalize to the same resolution and we see that the new PowerVR graphics setup is 57% faster than even ARM's Mali-T604 in the Nexus 10. Once again we're seeing just about 2x the performance of the previous generation iPad. Vsync bound gaming performance obviously won't improve, but the offscreen classic test gives us an idea of how well the new SoC can handle lighter workloads: For less compute bound workloads the new iPad still boasts a 53% performance boost over the previous generation. Ultimately it looks like the A6X is the SoC that the iPad needed to really deliver good gaming performance at its native resolution. I would not be surprised to see more game developers default to 2048 x 1536 on the new iPad rather than picking a lower resolution and enabling anti-aliasing. The bar has been set for this generation and we've seen what ARM's latest GPU can do, now the question is whether or not NVIDIA will finally be able to challenge Imagination Technologies when it releases Wayne/Tegra 4 next year. 
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| Google Nexus 4 and Nexus 10 Performance Preview Posted: 02 Nov 2012 08:00 AM PDT Earlier this week Google announced two new flagship Nexus devices: the Nexus 4 smartphone and the Nexus 10 tablet. We received review samples of both earlier this week, and while we're hard at work at full reviews of the devices we couldn't help but share all of the test data we've been able to amass at this point. For those who aren't familiar with it, the Nexus 4 features Qualcomm's Snapdragon S4 Pro SoC - a quad-core 28nm Krait CPU with Qualcomm's next-generation Adreno 320 GPU. The combination proved quite formidable in the MDP/T we tested, as well as LG's recently announced Optimus G. The SoC drives a 4.7-inch 1280 x 768 IPS display and is paired with 2GB of LPDDR2 memory. The Nexus 4 ships unlocked with 8GB of NAND for $299 without a contract ($349 for the 16GB version). Pair that with DC-HSPA+ support and you get an absolute killer smartphone for use on T-Mobile: no contracts, very low monthly fees, and compelling cellular performance: Brian will talk more about the combination in his full review, but rest assured that the lack of LTE is workable depending on T-Mobile coverage where you live/travel to. The Nexus 10 also boasts a brand new SoC: Samsung's Exynos 5 Dual. The Exynos 5 Dual features two ARM Cortex A15 cores running at 1.7GHz as well as ARM's own Mali-T604 GPU. This happens to be the exact same platform used in the new Chromebook, just running Android. The Nexus 10 features a 10.1-inch 2560 x 1600 display, giving it the same resolution as the 13-inch MacBook Pro with Retina Display - but in an even smaller form factor. Google is also aggressive on Nexus 10 pricing: the 16GB WiFi-only tablet sells for $399, with the 32GB version going for $499. Both Nexus devices run Android 4.2 and are guaranteed to be the first devices to be updated to upcoming Android revisions for the foreseeable future (it's the power of Nexus). We haven't had a ton of time to test the devices and put this together so you're going to see combined performance charts throughout the rest of this article. Read on for our quick analysis! 
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