Increasing Awareness of Energy Consumption in Jupyter Notebooks

by Marcel Garus · 2022-04-15 · 17 minute read · university stuff · available at mgar.us/jupyter-energy

Jupyter Notebooks are becoming an increasingly popular tool: These Python-based notebooks run in your browser and combine running code with writing explanatory documentation. Notebooks have a client-server architecture – even if they run on a powerful machine, you can still write your code on a light endpoint, such as a laptop. Free Jupyter Notebook services such as Google Colab make computing-intensive research fields more accessible to a general audience, but they also hide the amount of power consumed. If you're programming on your laptop, you might not even notice that the actual computing part requires a significant amount of resources in a data center. It doesn't help that Jupyter Notebooks are most commonly used in data science and Machine Learning, two of the most power-hungry disciplines. Hence, in my last semester, I developed an extension for Jupyter Notebooks that alerts you of your energy consumption.

The most similar extension is called Jupyter Resource Usage and uses psutil to retrieve data from the kernel infrastructure. That allows it to monitor RAM and CPU usage, but other resources are not supported – not even GPUs, which play a big part in training Machine Learning models.

Getting the energy consumption

Unfortunately, there is no established unified way of getting information about energy consumption from the kernel. I implemented getting data from several sources The Operating Systems and Middleware chair at my university developed an

Inspired by pinpoint, an energy measurement tool developed at the Operating Systems and Middleware chair of my university, I implemented getting data from several sources. I'd also like to give a shoutout to Sven Köhler, who not only developed this tool, but also looked after me and my project specifically. He was a big help in getting started with measuring energy and had deep knowledge about how energy is measured internally and what factors might influence measurements.

These are the measurement sources I integrated into the tool:

Running Average Power Limit

Linux offers a Running Average Power Limit (RAPL for short) on x86_64 CPUs. This RAPL allows tracking of the power consumption of CPU components, such as the CPU, RAM, or built-in GPU. Notably, it doesn't include external components like external graphic cards, connected peripherals, etc.

On Linux, for each trackable metric, there are several files in /sys/bus/event_source/devices/power/events. For example, on my laptop, the following files exist:

marcel@marcel-laptop:/sys/bus/event_source/devices/power/events$ ls
energy-cores        energy-gpu        energy-pkg        energy-psys        energy-ram
energy-cores.scale  energy-gpu.scale  energy-pkg.scale  energy-psys.scale  energy-ram.scale
energy-cores.unit   energy-gpu.unit   energy-pkg.unit   energy-psys.unit   energy-ram.unit

According to the Linux source code, these correspond to the following sources:

  • energy-cores: all physical cores

  • energy-gpu: the builtin GPU

  • energy-pkg: the whole processor package

  • energy-psys: the builtin psys domain

  • energy-ram: the RAM component

For each source, there are three files:

  • .../<event>: A file containing a hexadecimal event code. For example, my energy-cores file contains event=0x01.

  • .../<event>.scale: A file containing a scaling factor. On my laptop, the energy-cores.scale file contains 2.3283064365386962890625e-10.

  • .../<event>.unit: A file containing the unit in which the RAPL measures the energy consumption. Usually, this will be Joules.

You can use these file contents to make the Linux kernel measure how much energy the sources use. In particular, you can perform a perf_event_open syscall with the event code. This syscall will return a filehandle that contains an event counter for that event – that's just a number you can multiply by the scale to get the energy consumption in the given unit.

Here's what a minimal C program looks like that measures the energy consumption of a component:

struct perf_event_attr attr;  // perf_event_attr from #include <linux/perf_event.h>
memset(&attr, 0, sizeof(attr));
attr.type   = type;   // type from /sys/bus/event_source/devices/power/type
attr.size   = sizeof(attr);
attr.config = config; // config from /sys/bus/event_source/devices/power/events/<event>

long fd = syscall(
    __NR_perf_event_open, // perf_event_open syscall
    &attr,
    -1, // restricting to a pid is not supported
    0,  // not running on a particular cpu
    -1, // group_fd is not supported
    0   // no flags
);

long int counter_before;
read(fd, &counter_before, sizeof(long int));

sleep(10);

long int counter_after;
read(fd, &counter_after, sizeof(long int));

close(fd); // stops measuring

// scale from /sys/bus/event_source/devices/power/events/<event>.scale
double used_energy = (double)(counter_after - counter_before) * scale;

// unit from /sys/bus/event_source/devices/power/events/<event>.unit
printf("In 10 seconds, you used %0.3f %s.\n", used_energy, unit);
// "In 10 seconds, you used 3.458 Joules."

Microchip MCP39F511N Power Monitor

The Operating Systems and Middleware chair has a Microchip MCP39F511N Power Monitor (which we call MCP). That's actual physical hardware that you can plug between the wall socket and the computer. It then measures the power consumption of the entire system with all components, including external peripherals like connected displays, disks, or USB drives.

Here's a photo of the MCP:

The MCP connects the wall socket with the device to test. Via USB, you can get the measured energy consumption.

When you connect the MCP's USB port to a PC, it will appear at /dev/ttyACM0 (or with a higher number at the end). Pinpoint contains a small C library for communicating with the MCP over this serial interface – the protocol it uses is defined in the MCP's datasheet. A rudimentary usage of the RAPL without error-handling looks like this:

long fd = f511_init("/dev/ttyACM0");

int data[2]; // The MCP has two outlets where you can measure.
int result = f511_get_power(&data[0], &data[1], fd);

close(fd);

// The MCP returns the current power consumption in 10mW steps.
double watts = 0.01 * (double)data[0];
printf("The MCP's first channel is currently drawing %0.3f watts.\n", watts);

Contrary to the RAPL, the MCP only reports the power draw right now instead of a cumulative measure. Therefore, you need to continuously ask the MCP for measurements to gauge how much energy long-running tasks consume.

Nvidia Management Library

Finally, I looked at the Nvidia Management Library (NVML). In Python, the py3nvml package allows us to request the self-reported energy usage of Nvidia GPUs:

from py3nvml import py3nvml as nvml

device = nvml.nvmlDeviceGetHandleByIndex(gpu_index)
watts = nvml.nvmlDeviceGetPowerUsage(device) / 1000

It doesn't get much easier than this!

Building an Extension

Now that we know how to get the energy from several sources, we need to somehow show that data in Jupyter Notebooks. Those support two types of extensions:

  • server extensions: These types of extensions run in the Juypter Notebook process itself – it's running on the machine that executes the Python code. Because the Jupyter Notebook server is written in Python, you install these extensions as Python modules.

  • notebook extensions: These extensions run in the client's browser. They are written in JavaScript and can interact with the notebook the same way that the user can.

To record the energy data and display it, we need both types of extensions. By the way: The Jupyter Resource Usage also uses this approach – it was a helpful reference. One difference to that extension is that the perf_event_open syscall can only be executed as root unless you change proc/sys/kernel/perf_event_paranoid to allow more processes to listen for hardware events. Therefore, I put the energy data gathering in a separate process, the energy server. This separation allows the energy server to run as root without also running the Jupyter Notebook server as root (and thereby all the code written inside notebooks).

The energy server aggregates energy consumption data from multiple sources, saving both a short-term history of the power draw and a long-term recording of the energy usage. It communicates with sources in different ways: Accessing the RAPL and the MCP works best in C, so I wrote small C wrappers that can be compiled into shared libraries (with something like gcc --shared rapl.c -o rapl.so). The energy server written in Python can then call the defined C functions using Foreign Function Interfaces (FFI). For the NVML, I directly used the existing Python library.

The Jupyter Energy server extension runs in the Jupyter Notebook process and communicates with the energy server using HTTP. It also registers an HTTP endpoint in the server so that the frontend can make HTTP requests to the extension.

The Jupyter Energy notebook extension runs in the browser. It adds a button to the notebook's toolbar that shows how much power the computer currently draws and how much energy it used since the notebook was opened. If you click on the button, it opens a popup with historical information.

Here's an overview of the architecture:

The architecture of the Jupyter Energy extension. An energy server runs as root and communicates with various sources over FFI or standard Python function calls. Part of the extension lives in the Jupyter Notebook server, where it makes values available to clients via HTTP. Notebooks can request data from the extension in the Juypter Notebook server and display the consumption.

And here's how it looks:

A screenshot of the extension running. In the top right of the notebook, a button says

This image shows another popup with a different comparison text:

It also shows comparison values with emojis. Some of these references are from public sources (for example, how much energy the sun produces or how much energy it takes to bake a pizza). Other comparisons I measured with the MCP at home (such as the power consumption of my electric piano or water boiler).

If you switch to the long-term graph, the extension shows how that energy probably got generated. Of course, the extension doesn't know your current electricity contract and can only approximate the sources. All data comes from the European Network of Transmission System Operators for Electricity (ENTS-OE). That's a collection of companies that take care of transferring energy through Europe to meet demand. All data is publicly available at transparency.entsoe.eu. The extension aggregates sources into four types:

  • renewables: solar, wind, biomass, geothermal, water, and waste

  • non-renewables: fossil and nuclear

  • storage sources: reservoirs

  • other: sources that could not be classified or that are unclear to the ENTS-OE

Currently, the extension is hardcoded to load data for Germany. In the future, it could support other countries (the data for EU countries is already public) and be more precise within a country.

Evaluation

To assess if the recorded energy consumption is accurate and to measure the overhead of measuring energy, I compared the different supported sources in some benchmarks.

I measured on my Asus ZenBook 14 laptop with Ubuntu 20.04.3. I disabled many factors that may affect energy usage and put the device into a well-defined state to get good results:

  • no power savings (BIOS)

  • fully charged

  • no plugs (USB, HDMI) except the power cable

  • full brightness on screen and keyboard

  • Bluetooth off

  • no GUI (everything in terminal mode)

I could not eliminate all factors. The biggest remaining ones are wifi (because the notebook needed to be accessible from other devices in the network) and critical system services. I ran the Jupyter Notebook on a single core (pinned using numactl -C 1 jupyter notebook) to get more predictable results.

This setup allows me to compare the internally reported energy consumption (from the RAPL) with the one measured externally (with the MCP):

The MCP sits between the wall and the laptop. The laptop has a Juypter Notebook with the extension running and offers it publicly over wifi. Another PC has the notebook open and connects to the MCP. It can therefore relate the external energy measurements to the internal measurements.

To put some load on the system, I used the following benchmarks:

  • idle: Just running a notebook with a sleep(60) as a baseline of energy usage.

  • k-means: A common clustering approach from data science that is memory-bound. I used an implementation from the SciPy benchmark.

  • BLAS/LAPACK: The Basic Linear Algebra Subprograms & Linear Algebra PACKage, a set of linear algebra libraries implemented for many languages. The implementation is from the SciPy benchmark as well.

  • bible: A benchmark querying n-grams as search terms against a rudimentary database index. This was especially interesting to me because this program comes from the Information Retrieval seminar from a previous semester when I first got in contact with Jupyter Notebooks at university.

These are the results visualized in a graph (note that the time does not start at zero):

A graph with time on the x-axis and energy consumption on the y-axis. Dots and triangles are sprawled across that plane, each one corresponding to a measurement of a benchmark with a specific duration and energy consumption.

Each dot corresponds to a benchmark run that took a certain amount of time and energy. For those runs where the extension is activated, we have internal and external measurements; for those runs where it's deactivated, we only have external energy measurements.

Internal vs. external: Comparing the internal (RAPL) vs. the external (MCP) measurements, we can see that the externally measured consumption is generally higher – about seven times higher in the idle state and 1.2 to 2.0 times higher in the other benchmarks. That's expected: The RAPL only measures the CPU component; the MCP measures the power consumption of the whole laptop, including keyboard illumination, display, wifi chip, etc. In the idle state, the CPU is not used a lot, so it's only a small part of the energy usage.

With vs. without extension: The setup also allows us to compare the energy consumption and runtime with the extension enabled and disabled. This allows us to measure the overhead of measuring – measureception! Luckily, when enabling the extension, there are only minor changes in energy use (-0.7 %) and time (+0.6 %, excluding idle, +1.5 % excluding idle & bible). This indicates the extension supports everyday usage without massive energy or performance impacts.

Noisiness of benchmarks: Another observation is that the benchmarks differ in how noisy they are. The idle state is not noisy – that's because it only consists of a call to sleep, and therefore, it's not CPU-bound, but time-bound; even differences in other computing loads won't affect the runtime of this benchmark a lot. The other benchmarks generally tend to get noisier the longer they take. That is also expected – a longer runtime leaves more opportunity for unpredictable slowdowns.

Future Work

There are lots of areas where the extension can be improved:

  • Give more information about energy generation: Data about how much energy comes from wind, solar, etc. is already available. Maybe it would make sense to display that in the extension. Also, the generation estimation is currently only for Germany as a whole. It may make sense to extend this to more countries and to improve the approximation by taking into account a more precise location or even the electricity contract.

  • Highlight monetary motivation: You could allow the user to enter an electricity price to automatically convert the amount of energy consumed into the added cost on the electricity bill.

  • Make the installation easier: The installation experience can be improved by turning the extension into a package to be published on a Python package manager such as pip.

  • Conduct user studies: An under-explored aspect is whether the extension encourages people to use less energy. A study could be conducted by having a hidden version of the extension that measures the consumption silently but discloses the results only to the study investigators. We are already in the process of inquiring if we can conduct such a study in a data science seminar – stay tuned!

If you feel like contributing, feel welcome to have a look at the repository.

Reflecting on Measuring Energy

Contrary to measuring CPU or RAM usage, measuring energy consumption is an area with less established standards – depending on the hardware, different libraries and services need to be consulted.

In another lecture this semester, we measured the energy consumption of microcontrollers instead of complex software – that was much more predictable. While you have total control over the hardware in an embedded setting, modern operating systems come with many power-saving strategies built in and you have to work against them to get reliable results. Otherwise, the operating system may seemingly randomly decide to change the CPU's clock frequency or turn on a fan.

This unpredictability of behavior also makes it hard to attribute energy consumption to individual processes: While you can count the CPU cycles spent or RAM allocated by a process, the energy usage depends on many factors. For example, the fan turning on (and thereby consuming energy) is often not the result of a single process but the interaction of many processes running simultaneously.

That being said, there would be a tremendous value to even just an approximation of the energy usage of individual processes. For instance, cloud providers currently use CPU cycles and RAM for billing purposes. A billing model based on energy consumption may better reflect their costs and encourage users to measure the energy consumption of their code. The current state of tooling for measuring the energy efficiency of code still leaves a lot to be desired.

Let's hope this changes soon – I'm looking forward to a future with more energy-aware computing.

Thanks for reading!

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By the way, I wrote other articles about university stuff. Here's an article I recommend:

Encouraging People to Be More Careful in Situations With High Infection Risk

2022-03-21 · 18 minute read · university stuff

As you might have noticed, we are currently in a pandemic. Luckily, there are several steps you can take to protect yourself and others: You can get vaccinated, wear a mask, avoid large groups of people, regularly ventilate when being indoors with others, etc. Some of these measures are easier to follow than others. Getting vaccinated is a one-off action, but remembering to open the window every few minutes is a lot harder if you also concentrate on something else, such as working or studying.

In the context of the Sonic Thinking and Neurodesign lectures at our university, I developed an app that continuously evaluates the current infection risk and turns it into music.

The aspirational goal of the project is to enable scenarios like these:

  • You walk into an office that hasn’t been ventilated for a long time. As soon as you step inside, scary music starts to play, like you're in a horror film.

  • Over one hour, your study room gradually fills with people. An alarming tune slowly fades in and gets more dissonant the more people there are.

The Coronoise app takes incidence rate, number of people, and CO₂ levels as inputs and produces sounds.