What Does the OS X Activity Monitor’s “Energy Impact” Actually Measure?

https://blog.mozilla.org/nnethercote/2015/08/26/what-does-the-os-x-activity-monitors-energy-impact-actually-measure/

by nnethercote • 11 years ago

137 65 11 years ago

blog.mozilla.org

qiushihe• 11 years ago

The first sentence of the article:

Activity Monitor is a tool that was introduced in Mac OS X 10.9.

Activity Monitor was introduced with OS X 10.3 (https://en.wikipedia.org/wiki/Activity_Monitor). And was significantly revamped with OS X 10.9 to receive the various energy related measurements.

nnethercote7• 11 years ago

I'm the author of the post. You're right. I corrected the first paragraph.

Thank you for the suggestion.

icefox2• 11 years ago

I'm surprised that the author hasn't mentioned the positive effect it has had. After upgrading the OS and seeing the new menu entries I reported a number of applications that would show up as using a lot of energy and within a few releases there was a change note usually mentioning some simple fix which dramatically reduces the wake up's of the application or removing a long running animation that didn't add any value. This little menu addition has probably helped the battery life for macbook users more than any other change.

wmf• 11 years ago

I suspect that's the real reason why Apple is weighting wakeups heavily and exaggerating the energy impact: it shames developers into making their apps more efficient.

anologwintermut• 11 years ago

Except Chrome, which on every laptop I've ever used seems to decrease battery life by about a 1/3rd compared to Safari and is always marked as using significant power. (Currently 10.9.5 with chrome 44 on a 2014 macbook air, but I've had the issue on newer computers at work)

nnethercote7• 11 years ago

Exposing power consumption data is a great idea.

Exposing inaccurate and opaquely-computed power consumption data is a less great idea.

Someone• 11 years ago

I am not sure they are weighting wakeups heavily. "but with a “tax” of 500 microseconds for each wakeup" could be a reasonable estimate of the time the OS needs after wakeup before it can hand over the CPU to the process that did the wake up. That time isn't spend in the process that wakes up the system, but can be attributed to it.

ejdyksen2• 11 years ago

I could have sworn I read somewhere that Activity Monitor also included GPU usage in its measurements—naturally, using the GPU more uses more power/battery.

kitsunesoba• 11 years ago

I imagine that other things like WiFi usage, disk usage, and possibly even port usage could be factored in as well.

bigiain2• 11 years ago

I'd also guess backlight.

comex• 11 years ago

It does. I found a list of factors and posted it as a comment on the blog post:

https://blog.mozilla.org/nnethercote/2015/08/26/what-does-th...

In the data I posted, which is from /usr/share/pmenergy/default.plist, kgpu_time is 0.0, but in all the other plists it's nonzero.

ejdyksen2• 11 years ago

Oh wow, nice find. It looks like that calculation is pretty comprehensive, then.

nnethercote7• 11 years ago

I've updated the post to incorporate your findings. Thank you!

zurn• 11 years ago

Or possibly saves power, if work is being offloaded from the CPU.

travjones• 11 years ago

Take home point: "In fact, POWER* is a unitless measure because it is a semi-arbitrary combination of two measures with incompatible units."

*POWER = "Energy Impact."

nnethercote7• 11 years ago

For 10.9, POWER and "Energy Impact" appear to be the same. For 10.10 "Energy Impact" has changed.

kevinchen• 11 years ago

Since the formula is

Power = ((used_us + IDLEW * 500) * 100.0) / elapsed_us

If you believe that each idle wake costs you on average the same energy as 500us of computation, then the units are compatible right?

grecy• 11 years ago

Recent Intel hardware provides high-quality estimates of processor and memory power consumption ... But the big problem is that they are machine-wide measures that cannot be used on a per-process basis.

Would it not be possible for the OS to poll the CPU for these power consumption stats, and attribute the value returned to the currently running process?

Over time, I think it would be possible to see how much power the Intel CPU thinks each process is using.

nnethercote7• 11 years ago

If you poll with high frequency you'll be causing lots of additional wake-ups which will badly skew what you're measuring.

pjc50• 11 years ago

Ideally you'd do an accounting update on task switch, along with all the other housekeeping. Then you don't need to do any polling. There's a "process accounting" infrastructure which perhaps could be adapted for this.

cbsmith3• 11 years ago

Wakeups are a bit tricky to actively measure, because with the Power Nap feature, the actual # of wakeups triggered by a particular application is a bit trickier to measure and varies based on what other activities are going on the system.

In general, from the get go, it is a bit of a myth that you can really know how much of a power budget is a consequence of a particular application. You can get a rough sense of relative impact on the overall power budget, but even that can be seriously skewed by a LOT of factors. At best, you can get a sense of, "if I sampled at the moment power stores hit a multiple of X, how often would I see the system doing something on behalf of each app that was draining power at that moment". Even that, is bloody hard to pull off, but it is your best "rough" approximation of what is going on.

digitalengineer• 11 years ago

Is there anything like this for iOS? I'd love to know the consumption of energy (and data) for all my iOS apps!

shalmanese• 11 years ago

Power: Settings->General->Usage->Battery Usage

Data: Settings->Cellular, scroll to the bottom

rainforest• 11 years ago

Work in bootstrapping energy consumption exists in academia; for example Pathak et al[0]. The changes in 10.10.4 could be an implementation of something along the same lines, by fitting a model to the measured power consumption.

As comex notes in the comments on the article, there appears to be a table of weights for various features, presumably obtained by regression.

[0] http://research.microsoft.com/en-us/people/mzh/eurosys-2012....

AnthonBerg2• 11 years ago

Surely we can also measure actual heat and actual electricity usage? If not per program obviously, then as a reference or benchmark or calibration.

AnthonBerg2• 11 years ago

Downvote?

Let me rephrase: There are temperature and battery charge sensors in the machines. We can use these to better calibrate the "virtual" energy usage metrics.

DasIch• 11 years ago

These only help you determine the state of the entire system. They provide no information about the impact individual applications or processes have especially not relative to each other.

kec• 11 years ago

You can't use temperature to accurately model power consumption, if for no other reason than that it's too heavily influenced by environmental factors.

"Battery charge" sensors are problematic because they're hard to keep in calibration without interrupting normal operation of the system.

What Does the OS X Activity Monitor’s “Energy Impact” Actually Measure?

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