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Tegra 3: The Quad-Core SoC That Goes To Five

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By
SoC
Apple A5XTegra 3
Fab Node
45 nm40 nm
Processor
1 GHz ARM Cortex-A9 (dual-core)1.4 GHz ARM Cortex-A9 (quad-core)
Graphics
PowerVR SGX543MP4 (quad-core)ULP GeForce
L1 Cache
(Instruction/Data)
32 KB / 32 KB32 KB / 32 KB
L2 Cache1 MB1 MB


Tegra 3 (code name: Kal-El) isn’t particularly new to us. We've already run demos on devices and discussed this architecture prior to today's review. However, the iPad 3's introduction as a rival sparks renewed interest in how Nvidia’s architecture compares to Apple’s A5X.

GeekBench v2.2.7 Results
iPad 2
iPad 3
Dell Mini 1012
LePan II
Transformer Prime
CPU
Apple A5
Apple A5X
Atom N450
APQ8060
Tegra 3
Architecture
Dual-core A9
Dual-core A9
Single-Core Atom
Dual-core ScorpionQuad-core A9
Speed
1 GHz1 GHz1.66 GHz1.2 GHz1.4 GHz
Overall
764
760
917
649
1194
Integer
691
687
910
709
1781
Floating Point
921
920
762
943
1781
Memory
830
825
1105
362
1091


In terms of raw processing potential, Tegra 3 leads the pack by a large margin. Software optimizations and clock rates aside, increased parallelization allows Nvidia's SoC to work on more data concurrently. Similar to the desktop space, adding cores doesn't turn out to have a multiplicative effect on most real-world applications. But an enhanced ability to multitask is nice, especially as resource-hungry background tasks pile up.

Of course, bolstering performance often incurs higher power consumption at the same time. Nvidia, anticipating this, addressed power from a creative angle.

Kal-El
Companion CPU Core
Main CPU Cores (Symmetric Processing)
# of Cores
1
4
Function
Power-Optimized (Standby)
Performance
Architecture
Cortex A9
Cortex A9
Process Technology
Low Power (LP)
General
Operating Frequency
0 MHz to 500 MHz
0 MHz to Max Frequency


Kal-El sports a fifth "companion" CPU core that operates at lower frequencies and handles background tasks like syncing email, playing ringtones, and keeping applications alive while the device is in standby mode. It's hard to quantify the exact benefit of Nvidia's implementation since there aren't any Tegra 3s that lack the fifth core. However, the company's engineers clearly felt strong enough about its effect (particularly coupled with low-power silicon) that they were willing to dedicate precious die space to what was considered a power-optimized design.

Borrowing a page from Qualcomm's book, Nvidia employs an asymmetrical clock scheme that's similar to Turbo Boost, except that it allows the companion core to operate at a different frequency. It also incorporates Advanced SIMD (called NEON), which lets the CPU perform certain tasks (like playing MP3 audio) at extremely low CPU speeds, generally between 10-20 MHz. Qualcomm made a name for itself using a similar design, and the result is a processor with very low power consumption that can deliver performance when it's needed. Read Third-Generation Snapdragon: The Dual-Core Scorpion for more information on Qualcomm's solution.

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There’s every reason to believe that this hybrid approach should work well. However, realizing gains with this approach depends on Nvidia to work within the constraints of operating system design. Purposely, Tegra 3 doesn't expose the fifth CPU core to the OS. Rather, it operates in the background without any management from the operating system. That means “low-overhead tasks” have to be identified by the hardware and handled by its companion core.

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