How to harness the Powers of the Cloud TPU?



Introduction


About a couple of months ago, I got introduced to Google Colab (an enhanced version of JuPyteR notebooks) and since then didn’t look back. It’s got everything and more you need as a researcher. The initial idea was to load up python notebooks and run them on it. Soon we realised we can actually run those notebooks not just on CPUs available on GCP but also GPUs and TPUs. Also, read up a bit about it from other sources, see Google Reveals Technical Specs and Business Rationale for TPU Processor (slightly dated, but definitely helpful).


Here we go now…


What is a TPU?

Just like a GPU is a graphics accelerator ASIC (to help create graphics/images quickly for output to a display device) — which since long have been discovered that can be taken advantage of by using it for massive number crunching. Similarly, a TPU is an AI accelerator ASIC developed by Google specifically for Neural Network Machine Learning. One of the differences being TPUs are more about processing high-volume low-precision computation while GPUs for high-volume high-precision computation (please check the Wikipedia links for the interesting differences).


Then what?


TL;DR — how the notebooks and slides came about


To understand how these devices work, what better approach can we adopt than to benchmark them and then compare the results. Which is why we had a number of notebooks that came out of these experiments. And then we were also coincidentally preparing for Google Cloud Next 2018 at the Excel Center, London. And I spent an evening and a weekend preparing the slides for the talk Yaz and I were asked to give — Harnessing the Powers of Cloud TPU.


What happened first, before the other thing happened?


TL;DR — how we work at the GDG Cloud meetup events


It was a mere coincidence while we were meeting regularly at the GDG Cloud meetups in the London chapter, where Yaz would find interesting things to look at during the hack sessions (Pomodoro sessions — as he called them), suggested one session that we play with TPUs and benchmark them. Actually, I remember suggesting we do this during our sessions as an idea, but then we all got distracted with other equally interesting ideas (all saved somewhere on GitLab). And then I frantically started playing with two notebooks related to GPU and TPU respectively, provided as examples by Colab, which I then got to work on the TPU and then adapted it to work on the GPU (can’t remember anymore which way first). They both were doing slightly different things and measuring the performance of the GPU and TPU and I decided to make them do the same thing and measure the time taken to do it on the different device. Also, display details about the devices themselves (you will see towards the top or bottom of each notebook).


CPU v/s GPU v/s TPU — Simple benchmarking example via Google Colab


CPU v/s GPU — Simple benchmarking


The CPU v/s GPU — Simple benchmarking notebook finish processing with the below output:

TFLOP is a bit of shorthand for “teraflop”, which is a way of 
measuring the power of a computer based more on mathematical 
capability than GHz. A teraflop refers to the capability of a 
processor to calculate one trillion floating-point operations
per second.
CPU TFlops: 0.53 
GPU speedup over CPU: 29x                    TFlops: 15.70

I was curious about the internals of the CPU and GPU so I ran some Linux commands (via Bash) that the notebooks allow (thankfully) and got these bits of info to share:



You can find all those commands and the above output in the notebook as well.


CPU v/s TPU — Simple benchmarking


The TPU — Simple benchmarking notebook finish processing with the below output:

TFLOP is a bit of shorthand for “teraflop” which is a way of 
measuring the power of a computer based more on mathematical 
capability than GHz. A teraflop refers to the capability of a 
processor to calculate one trillion floating-point operations
per second.
CPU TFlops: 0.47
TPU speedup over CPU (cold-start): 75x        TFlops: 35.47 
TPU speedup over CPU (after warm-up): 338x    TFlops: 158.91

Unfortunately, I haven’t had a chance to play around with the TPU profiler yet to learn more about the internals of this fantastic device.

While there is room for errors and inaccuracies in the above figures, you might be curious about the tasks used for all the runs — it’s the below piece of code that has been making the CPU, GPU and TPU circuitry for the Simple benchmarking notebooks:


def cpu_flops():
  x = tf.random_uniform([N, N])
  y = tf.random_uniform([N, N])
  def _matmul(x, y):
    return tf.tensordot(x, y, axes=[[1], [0]]), y
return tf.reduce_sum(
    tf.contrib.tpu.repeat(COUNT, _matmul, [x, y])
  )

CPU v/s GPU v/s TPU — Time-series prediction via Google Colab


Running the TPU version of the Timeseries notebook gave us some issues initially, which was reported on a StackOverflow post and a couple of good folks from the Google Cloud TPU team stepped in to help. But we managed to get the GPU version of the Time-Series Prediction notebook to work which clearly showed a much better response than the CPU version of Time-Series Prediction notebook — this version just choked half-way through the CPU-cycles and Colab asked me if I wanted to stop the process because we needed more resources (more memory)!!!


Time series: GPU version


Here snapshots of the notebook (Train the Recurrent Neural Network section), the full notebook can be found on Google Colab, it’s free to download, share and extract the python code in it.


Epoch 1/10
 9/10 [==========================>...] - ETA: 4s - loss: 0.0047WARNING:tensorflow:Early stopping conditioned on metric `val_loss` which is not available. Available metrics are: loss
WARNING:tensorflow:Can save best model only with val_loss available, skipping.
WARNING:tensorflow:Reduce LR on plateau conditioned on metric `val_loss` which is not available. Available metrics are: loss,lr
10/10 [==============================] - 42s 4s/step - loss: 0.0048
Epoch 2/10
 9/10 [==========================>...] - ETA: 4s - loss: 0.0041WARNING:tensorflow:Early stopping conditioned on metric `val_loss` which is not available. Available metrics are: loss
WARNING:tensorflow:Can save best model only with val_loss available, skipping.
WARNING:tensorflow:Reduce LR on plateau conditioned on metric `val_loss` which is not available. Available metrics are: loss,lr
10/10 [==============================] - 42s 4s/step - loss: 0.0041
Epoch 3/10
 9/10 [==========================>...] - ETA: 4s - loss: 0.0047WARNING:tensorflow:Early stopping conditioned on metric `val_loss` which is not available. Available metrics are: loss
WARNING:tensorflow:Can save best model only with val_loss available, skipping.
WARNING:tensorflow:Reduce LR on plateau conditioned on metric `val_loss` which is not available. Available metrics are: loss,lr
10/10 [==============================] - 42s 4s/step - loss: 0.0046
Epoch 4/10
 9/10 [==========================>...] - ETA: 4s - loss: 0.0039WARNING:tensorflow:Early stopping conditioned on metric `val_loss` which is not available. Available metrics are: loss
WARNING:tensorflow:Can save best model only with val_loss available, skipping.
WARNING:tensorflow:Reduce LR on plateau conditioned on metric `val_loss` which is not available. Available metrics are: loss,lr
10/10 [==============================] - 43s 4s/step - loss: 0.0039
Epoch 5/10
 9/10 [==========================>...] - ETA: 4s - loss: 0.0048WARNING:tensorflow:Early stopping conditioned on metric `val_loss` which is not available. Available metrics are: loss
WARNING:tensorflow:Can save best model only with val_loss available, skipping.
WARNING:tensorflow:Reduce LR on plateau conditioned on metric `val_loss` which is not available. Available metrics are: loss,lr
10/10 [==============================] - 44s 4s/step - loss: 0.0048
Epoch 6/10
 9/10 [==========================>...] - ETA: 4s - loss: 0.0036WARNING:tensorflow:Early stopping conditioned on metric `val_loss` which is not available. Available metrics are: loss
WARNING:tensorflow:Can save best model only with val_loss available, skipping.
WARNING:tensorflow:Reduce LR on plateau conditioned on metric `val_loss` which is not available. Available metrics are: loss,lr
10/10 [==============================] - 44s 4s/step - loss: 0.0037
Epoch 7/10
 9/10 [==========================>...] - ETA: 4s - loss: 0.0042WARNING:tensorflow:Early stopping conditioned on metric `val_loss` which is not available. Available metrics are: loss
WARNING:tensorflow:Can save best model only with val_loss available, skipping.
WARNING:tensorflow:Reduce LR on plateau conditioned on metric `val_loss` which is not available. Available metrics are: loss,lr
10/10 [==============================] - 44s 4s/step - loss: 0.0041
Epoch 8/10
 9/10 [==========================>...] - ETA: 4s - loss: 0.0037WARNING:tensorflow:Early stopping conditioned on metric `val_loss` which is not available. Available metrics are: loss
WARNING:tensorflow:Can save best model only with val_loss available, skipping.
WARNING:tensorflow:Reduce LR on plateau conditioned on metric `val_loss` which is not available. Available metrics are: loss,lr
10/10 [==============================] - 44s 4s/step - loss: 0.0038
Epoch 9/10
 9/10 [==========================>...] - ETA: 4s - loss: 0.0040WARNING:tensorflow:Early stopping conditioned on metric `val_loss` which is not available. Available metrics are: loss
WARNING:tensorflow:Can save best model only with val_loss available, skipping.
WARNING:tensorflow:Reduce LR on plateau conditioned on metric `val_loss` which is not available. Available metrics are: loss,lr
10/10 [==============================] - 44s 4s/step - loss: 0.0039
Epoch 10/10
 9/10 [==========================>...] - ETA: 4s - loss: 0.0036WARNING:tensorflow:Early stopping conditioned on metric `val_loss` which is not available. Available metrics are: loss
WARNING:tensorflow:Can save best model only with val_loss available, skipping.
WARNING:tensorflow:Reduce LR on plateau conditioned on metric `val_loss` which is not available. Available metrics are: loss,lr
10/10 [==============================] - 44s 4s/step - loss: 0.0035
CPU times: user 10min 8s, sys: 1min 22s, total: 11min 30s
Wall time: 7min 12s

The above run takes about ~7 mins (or total time of ~8 mins) on the Google Colab GPU:


CPU times: user 10min 8s, sys: 1min 22s, total: 11min 30s
Wall time: 7min 12s

I’m still unsure on how to interpret this time-related stats but I will take ~7 mins as our execution time till this point.


We finish with the following stats:

So now you can see why I earlier chose ~7 mins as the execution time. So it takes about 7 minutes to process this notebook — giving new predictions of temperature, pressure and wind speed and comparing it with the actual values (true values gather from post observations).


Time series: TPU version


Here snapshots of the notebook (Train the Recurrent Neural Networksection), the full notebook can be found on Google Colab, it’s free to download, share and extract the python code in it.

Found TPU at: grpc://10.118.17.162:8470
INFO:tensorflow:Querying Tensorflow master (b'grpc://10.118.17.162:8470') for TPU system metadata.
INFO:tensorflow:Found TPU system:
INFO:tensorflow:*** Num TPU Cores: 8
INFO:tensorflow:*** Num TPU Workers: 1
INFO:tensorflow:*** Num TPU Cores Per Worker: 8
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:CPU:0, CPU, -1, 11845881175500857789)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:XLA_CPU:0, XLA_CPU, 17179869184, 5923571607183194652)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:XLA_GPU:0, XLA_GPU, 17179869184, 11085218230396215841)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:TPU:0, TPU, 17179869184, 12636361223481337501)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:TPU:1, TPU, 17179869184, 14151025931657390984)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:TPU:2, TPU, 17179869184, 16816909163217742616)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:TPU:3, TPU, 17179869184, 4327750408753767066)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:TPU:4, TPU, 17179869184, 504271688162314774)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:TPU:5, TPU, 17179869184, 14356678784461051119)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:TPU:6, TPU, 17179869184, 6767339384180187426)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:TPU:7, TPU, 17179869184, 1879489006510593388)
INFO:tensorflow:*** Available Device: _DeviceAttributes(/job:worker/replica:0/task:0/device:TPU_SYSTEM:0, TPU_SYSTEM, 17179869184, 17850015066511710434)
WARNING:tensorflow:tpu_model (from tensorflow.contrib.tpu