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It appears that Tegra 2 is missing the ARM NEON SIMD engine (http://www.anandtech.com/show/4144/lg-optimus-2x-nvidia-tegra-2-review-the-first-dual-core-smartpho

It appears that Tegra 2 is missing the ARM NEON SIMD engine (http://www.anandtech.com/show/4144/lg-optimus-2x-nvidia-tegra-2-review-the-first-dual-core-smartphone/8 http://www.anandtech.com/show/4144/lg-optimus-2x-nvidia-tegr...) which the iPad 2's A5 chip supposedly has (someone please confirm this report: http://pdadb.net/index.php?m=cpu&id=a50000&c=samsung_apple_a5 http://pdadb.net/index.php?m=cpu&id=a50000&c=samsung...). This would explain the benchmark discrepancy. There is another benchmark (http://www.pcmag.com/article2/0,2817,2381767,00.asp http://www.pcmag.com/article2/0,2817,2381767,00.asp) that shows that A5 is 3x faster at matrix operations than Tegra 2, while being 1.5x slower executing code that likely does not involve matrix/vector operations.

DarkShikari 16y ago
Yes, Tegra 2 is missing NEON. I can't comprehend why people still release CPUs intended for any kind of performance yet omit the SIMD engine -- my suspicion is nVidia is trying to encourage developers to use their GPU APIs instead by crippling the ability of the CPU to do number crunching. I highly doubt it's an overly significant power or die size issue -- with the amount they're already spending on L1 cache, L2 cache, and so forth, it seems dumb to omit the kind of powerful ALU necessary to make use of it all.
- pmjordan 16y ago
  Is there a GPGPU API available on typical Tegra2 devices? OpenCL, CUDA? Without that, using the GPU for number crunching basically isn't going to happen.
- rsynnott 16y ago
  Tegra 2 doesn't support OpenCL or CUDA, though Tegra 3 will. The PowerVR SGX543 supports OpenCL, though not, of course, CUDA. EDIT: At the time, NVidia claimed that it _was_ a die size limitation.
modeless 16y ago
Lack of NEON can't explain these benchmark results. This is GPU-bound stuff. The PowerVR SGX 543 core is simply a better GPU than NVIDIA's Tegra 2 GPU, and the A5 has two of them. What's even more impressive is that Imagination Technologies claims this design can scale performance linearly up to 16 cores, for eight times the performance of the iPad 2 with no software changes. That headroom will come in handy for the inevitable retina display iPad.

DarkShikari 16y ago

Yes, Tegra 2 is missing NEON. I can't comprehend why people still release CPUs intended for any kind of performance yet omit the SIMD engine -- my suspicion is nVidia is trying to encourage developers to use their GPU APIs instead by crippling the ability of the CPU to do number crunching. I highly doubt it's an overly significant power or die size issue -- with the amount they're already spending on L1 cache, L2 cache, and so forth, it seems dumb to omit the kind of powerful ALU necessary to make use of it all.

pmjordan 16y ago
Is there a GPGPU API available on typical Tegra2 devices? OpenCL, CUDA? Without that, using the GPU for number crunching basically isn't going to happen.
rsynnott 16y ago
Tegra 2 doesn't support OpenCL or CUDA, though Tegra 3 will. The PowerVR SGX543 supports OpenCL, though not, of course, CUDA. EDIT: At the time, NVidia claimed that it _was_ a die size limitation.

modeless 16y ago

Lack of NEON can't explain these benchmark results. This is GPU-bound stuff. The PowerVR SGX 543 core is simply a better GPU than NVIDIA's Tegra 2 GPU, and the A5 has two of them. What's even more impressive is that Imagination Technologies claims this design can scale performance linearly up to 16 cores, for eight times the performance of the iPad 2 with no software changes. That headroom will come in handy for the inevitable retina display iPad.