Tensor Processing Unit
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Tensor Processing Unit (TPU) is an ASIC announced by Google for executing Machine Learning (ML) algorithms. CPUs are general purpose processors. GPUs are more suited for graphics and tasks that can benefit from parallel execution. DSPs work well for signal processing tasks that typically require mathematical precision. On the other hand, TPUs are optimized for ML. While any of the others could also be used for ML, TPUs are expected to bring better performance per watt for ML. In fact, TPUs are said to catapult computing power seven years into the future, which is equivalent to three generations of Moore's Law. Tests show a 14x better performance compared to GPUs.
What is Google's interest in making the TPU?
Google has claimed that "great software shines brightest with great hardware underneath." This is particularly true of ML where a TPU would offer software the requisite power to run faster and hence process more data. Google wants to use TPUs to power its ML algorithms. As of May 2016, more than 100 teams are said to be using ML within Google. Google Today, Street View, Inbox Smart Reply, RankBrain and voice search are products that are already benefiting from TPU hardware. AlphaGo used TPUs to defeat Go world champion Lee Sedol.
Beyond Google's internal projects, TPUs can offer an advantage for all ML applications implemented in TensorFlow. ML applications looking to run out of a cloud infrastructure will tend to prefer Google Cloud Platform powered by TPUs. Likewise, TPUs may be a differentiator for Google Cloud Platform when application developers select an ML service API for their applications. For example, Google Cloud Machine Learning is a managed ML service from Google that will directly benefit from TPUs.
Can TPUs be used for ML frameworks other than TensorFlow?
TensorFlow is not the only framework for ML. More specifically, there are multiple frameworks for Deep Learning (DL). However, Google has not disclosed if TensorFlow algorithms are hardwired in TPU or if TPU is a generic accelerator for ML.
How is TPU able to achieve its superior performance compared to other processor types?
Since TPU is an ASIC, optimization is hardwired into the chip. This gives it a speed advantage over CPUs, DSPs and GPUs. Compared to traditional ASICs, such as those used for video stream decoding, TPU's ability to process more data comes from the fact that it sacrifices precision. For example, instead of 32-bit processing, 8-bit processing may be employed and extra precision is used only when required. A TPU can therefore do more operations per second with the same amount of silicon. A TPU can be considered as an AI Accelerator that's emerging as a processor specialized to the task of Machine Learning and Artificial Neural Networks.
Doesn't low-precision arthimetric reduce accuracy of calculations?
Research has shown that deep learning algorithms are not affected by low-precision arithmetic. In fact, low-precision arithmetic can be used for both training as well as inference. This is because ML is essentially probabilistic in nature and high-precision arithmetic is unnecessary. One writer reported that "having more data that is less precise yield better results than having half as much data that was more precise." In fact, addition of noise during training can improve performance.
One report claimed that Google intends to use TPU only for inference. The report added that low-precision arithmetic is not suited for training. With the release of TPU2, it's clear that these can be used for both training and inference.
What's the competition for Google's TPU?
Google's TPU is in fact used only within Google, at least for now. Nvidia dominates the ML processor market with its GPUs. Nvidia has specialized its Tesla GPUs, named Pascal, that are suited for ML. These can be used either for training or for inference. Movidius makes Visual Processing Units (VPUs), named Myriad 2, that offer visual intelligence at device level. IBM's own chip named TrueNorth is based on a project that built the digital equivalent of a rodent's brain. TrueNorth is meant to bring deep learning to devices for the purpose of inference. Intel announced in November 2016 an AI processor named Nervana that may come to market end of 2017. Nervana is designed to be used for both training and inference. Microsoft for its part has been using FPGAs instead in its datacenters since these can be configured easily unlike ASICs. Configurability is an important aspect when algorithms change frequently and hence ASICs are not suitable. Qualcomm announced in January 2017 that it has optimized TensorFlow for the Hexagon 682 DSP. ARM is promoting its MALI GPUs to offload ML processing from its Cortex CPUs.
Is Google's TPU anyway connected to SGI's product of the same name?
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