GPU Performance: Tegra 2
As we’ve mentioned in the past, mobile devices like smartphones and tablets use highly integrated logic referred to as SoCs to minimize physical footprints and power consumption, all the while optimizing for performance and functionality. By putting execution resource, graphics processing, system memory, and several other subsystems in a single ASIC, data transfers can be achieved more efficiently without soldering a bunch of separate chips onto a PCB. Incidentally, the same SoC term applies to modern desktop processors like Intel's Sandy Bridge- and AMD's Bulldozer-based chips, which combine cores, cache, memory controllers, and other capabilities.
| SoC | Apple A4 (iPad) | Apple A5 | Nvidia Tegra 2 |
|---|---|---|---|
| Tablets | Apple iPad | Apple iPad 2 | Acer Iconia Tab A500Asus Eee Pad TransformerMotorola XoomMotorola Xoom Family EditionSamsung Galaxy Tab 10.1Toshiba Thrive |
| Processor | 1 GHz ARM Cortex-A8 (single-core) | 1 GHz ARM Cortex-A9 (dual-core) | 1 GHz ARM Cortex-A9 (dual-core) |
| Memory | 256 MB 333 MHz LP-DDR (single-channel) | 512 MB 1066 MHz LP-DDR2 (dual-channel) | 1 GB 667 MHz LP-DDR2 (single-channel) |
| Graphics | PowerVR SGX535 (single-core) | PowerVR SGX545MP2 (dual-core) | ULP GeForce (single-core) |
| L1 Cache(Instruction/Data) | 32 KB / 32 KB | 32 KB / 32 KB | 32 KB / 32 KB |
| L2 Cache | 640 KB | 1 MB | 1 MB |
Tegra is Nvidia’s SoC brand, and it represents the company’s effort to tap into the mobile market beyond its desktop-derived GeForce graphics processors. For those unfamiliar with Tegra 2, read page eight of our Motorola Xoom review for a full discussion of GPU architecture. On the CPU side, Tegra 2 shares the same dual-core Cortex-A9, which offers a substantial boost from Cortex-A8 used in the first-generation iPad. Read Apple's iPad 2 Review: Tom's Goes Down The Tablet Rabbit Hole for a full discussion of Cortex-A9 performance.
While we've already covered Tegra 2, it's important to examine the graphics performance of each tablet. Sy Choudhury, director of product management at Qualcomm, once stated, "There is a misconception that the same processor and operating system gives the same performance." Why is wrong to expect the same performance from all Android-based Tegra 2 tablets? All hardware vendors get the same hardware optimizations from SoC developer, but not all of the software optimizations are enabled by OEMs.
| GPU (System-on-Chip) | PowerVR SGX 535 (Apple A4) | PowerVR SGX 543 (Apple A5) | ULP GeForce (Tegra 2) |
|---|---|---|---|
| SIMD | USSE | USSE2 | Core |
| Pipelines | 2 (unified) | 4 (unified) | 8 (4 pixel / 4 vertex) |
| TMUs | 2 | 2 | 2 |
| Bus Width (bit) | 64 | 64 | 32 |
| Triangle rate @ 200 MHz | 14 MTriangles/s | 35 MTriangles/s | ? |
The ULP GeForce has a maximum operating frequency of 300 MHz, but device vendors can tweak this setting to save on power. Nvidia provides less information on the Tegra 2 than it does for its desktop GPUs, so it’s best to move on to benchmarks. As with all of our tablet reviews, we're turning to GLBenchmark.
We know that the version of Tegra 2 in the Xoom is somewhat restricted. Motorola wants to emphasize better battery life, so it caps the Tegra 2's memory clock at 600 MHz, despite the fact that Nvidia specs the Tegra 2 for up to 667 MHz. This explains why other Android-based tablets, including the Xoom Family Edition, outperform the Xoom.
Compared to the competition, the Xoom Family Edition offers performance typical of a Tegra 2-based tablet. It's better than the iPad, but worse than the iPad 2. However, the standard Egypt and Pro tests only measure performance at a tablet's native resolution. On 10.1" Android-based tablets, that is always 1280x800 (compared to the iPad/iPad 2's 1024x768).
