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GPU Performance: Tegra 2

Acer Iconia Tab A500: A Tablet With Honeycomb 3.1
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As we’ve mentioned in the past, mobile devices like smartphones and tablets use what’s known as a system-on-chip (SoC). This integrates the processor, GPU, RAM, and several other subsystems onto single device. Since all of those components sit next to each other on the same chip, there is greater efficiency in data transfers, while reducing the amount of space consumed on the PCB.


Apple A4 (iPad)
Apple A5 (iPad 2)
Tegra 2 (Xoom/Iconia A500)
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 Cache640 KB
1 MB1 MB


Tegra is Nvidia’s SoC brand, and it symbolizes the company’s effort to tap into the mobile market beyond its desktop-derived GeForce graphics processors. A lot of engineering is tied up in this initiative, and what we see today in tablets like the Xoom represents the company's second incarnation of Tegra.

You may be asking "What happened to the first Tegra?" Flatly, it was far less impressive, even when it hit the market in 2009. Compared to Apple’s A4, it was a much more conservative design. Nvidia choose the older ARM11 processor, which probably explains the lack of design wins. Microsoft’s Zune HD was the only major product that employed the original Tegra.

Tegra 2Tegra 2

Tegra 2 is an entirely different beast. It’s based on the Cortex-A9, which is a generation ahead of the older ARM11. This is the same CPU seen in Apple’s A5 (iPad 2). Read Apple's iPad 2 Review: Tom's Goes Down The Tablet Rabbit Hole for a full discussion of Cortex-A9 performance.

Tegra 2: Graphics PipelineTegra 2: Graphics Pipeline

The ultra-low power GeForce isn't just a physically smaller GPU than the A5’s SGX 543MP2. Unlike Nvidia's desktop GPUs, Tegra 2 is based on an architecture that pre-dates its unified design. So, you’re looking at four pixel shader cores and four vertex shader cores. This means Tegra 2 operates most efficiently when it's presented with an even mix of vertex and shader code. We expect Nvidia to address that constraint in Tegra 3 (code named Kal-El).

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/s35 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 in our iPad 2 review, we're turning to GLBenchmark 2.0.

In terms of frames rendered in a set period of time, the Xoom and Iconia A500 offer more performance than the original iPad but both still falls short of the iPad 2. Interestingly, the Iconia A500 falls ever so slightly behind the Xoom. We don't have performance numbers for the Xoom after the 3.1 update, which makes this a difficult comparison. Google added a performance-oriented optimizations in 3.1 that explain the large delta.

GPU (System-on-Chip)
PowerVR SGX 535
(Apple A4)
PowerVR SGX 543
(Apple A5)
ULP GeForce (Tegra 2)
SIMD
USSE
USSE2
Core
Channels
Single
Dual
Single
Memory Bandwidth
2.6 GB/s
17.0 GB/s
2.6 GB/s


You can't use fill or triangle rates to draw a direct comparison of how well Tegra 2 utilizes its memory bandwidth, even though it's a quick-and-dirty way of sizing up other mobile GPUs.

GLBenchmark 2.0Apple iPad
(iOS 4.3)
Apple iPad 2
(iOS 4.3)
Motorola Xoom
(3.0)
Acer Iconia A500
(3.0)
Acer Iconia A500 (3.1)
Egypt frames (frames)
575
5075
1371
1202
2304
Egypt with FSAA (frames)
436
5057
--
-
Pro (frames)
880
2897
1347
1225
1865
Pro with FSAA (frames)
672
2851
--
-
Egypt with FSAA Fixed Time (sec)
825.6
65.0
--
-
Pro with FSAA Fixed Time (sec)
123.3
22.6
--
-
Swap Buffer Test (frames)
600
599
603
526
614
Fill Test (texture fetch) ktexel/s170980918551129897122164
16766
Trigonometric Test (vertex weighted) kvertex/s1039332626322292
3159
Trigonometric Test (fragment weighted) kfragment/s1191351244524577
563
Trigonometric test (balanced) kshader/s1259315825432600
311
Exponential Test (vertex weighted) kvertex/s3130353526282291
2781
Exponential Test (fragment weighted) kfragment/s37741116530032965
4961
Exponential Test (balanced) kshader/s20431173516561658
2575
Common Test (vertex weighted) kvertex/s1524372719732270
2477
Common Test (fragment weighted) kfragment/s1634369944514584
7964
Common Test (balanced) kshader/s1065411425302722
4513
Geometric Test (Vertex Weighted) kvertex/s1949377613161375
1465
Geometric Test (Fragment Weighted) kfragment/s2081638828882870
5639
Geometric Test (Balanced) kshader/s1281618116281638
3129
For Loop Test (Vertex Weighted) kvertex/s1671386013151373
1468
For Loop Test (Fragment Weighted) kfragment/s1842623772717202
11856
For Loop Test (balanced) kshader/s1275371835833604
5320
Branching Test (vertex weighted) kvertex/s3906377826332501
3443
Branching Test (fragment weighted) kfragment/s60452255732113153
3995
Branching Test (balanced) kshader/s21061119314931496
1858
Array Test (uniform array access) kvertex/s2918365839463438
5487
Triangle Test (white) ktriangle/s954829957125959708
14613
Triangle Test (textured, vertex lit) ktriangle/s705821129105209171
12517
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