On laptops, power management is a key feature to prolonge battery life as much as possible.
Monitoring power consumption can be done at the system level and each operating system has a flurry of tools to do it. The metrics you can use will produce very low-level metrics, like the Running Average Power Limit (RAPL) (https://01.org/rapl-power-meter) or higher level ones, like tracking CPU/GPU/Network/Disk usage at the process level.
For instance, Powertop (xxx) provides metrics similar to top, but focuses on what consumes energy. An application that uses a lot of RAM but idles will not impact energy by much, as opposed to one that uses 100% of the CPU and will eventually drain your battery. Tools like Powertop will point them as the cause of a sudden battery life drops.
In a perfect world, the newest Firefox uses one process per tab and all other tabs are happily idling in the background. The only one that is draining the battery is the active one. Background tabs might wake up from time to time, but will gently go back to sleep.
But that's far from reality. Modern web pages are dynamic and will use features like web sockets, background workers, notifications etc. They might suck your resources even if they are not the active tab.
A webmail client like gmail is a typical example. Even if the tab is in the background, it will stay active. If you activate Google Hangout, you are going to constantly interact with servers.
In Firefox, assuming es10 is the default, we can track a few metrics per tabs. As a matter of fact, "about:performance" is doing that in its "Performance of Web Pages" section. This section will display the CPU usage and impact on framerate (XXX see how its computed), among other metrics.
But that page is not focusing on power metrics. For instance it's not checking the network usage. (xxx verify this)
In that case, would it make sense to extend this feature and have a specialized "about:energy" page in Firefox, like what Powertop has at the OS level?
Or simply enhance "about:performance"?
Would this help tracking web pages that are responsible for reducing battery life? Can it lead to finding improvements in Firefox?
This document investigates whether it would make sense to add an "about:energy" page in Firefox to specifically track power used by tabs and how it could look like.
XXX talk about Chrome Task Manager. XXX
Measuring power at the process level is quite hard, and there's no precise correlation between what you can measure and the power consumption of a process -- and indirectly, how much it affects battery usage.
However, tracking a few metrics can give us some hints on which web pages are responsible for energy consumption, this is very interesting in particular if they are being active in the background.
A few useful per-process (per-tab) measures:
- CPU and GPU usage
- Wake-up counts / Low C-state residency
- Network activity
- Disk activity
- Tab in the foreground or background
If a tab has high values in some of those numbers, it's likely that it's causing more energy consumption than other processes.
One thing that's hard to define is some kind of formula or threshold. When can we flag a tab as being greedy? TBD
Even if tabs that are resources hogs can be detected, finding the root cause of the problem is hard, there's no silver bullet. If a web page starts to eat of lot of resources, more digging is required.
Finding the cause can be done with those tools: - Animation inspector - Profilers (gecko etc) - dtrace, perf, TimerFirings logging
XXX maybe we could have in about:energy a way to send logs when a tab is eating a lot of CPU, with some preliminary findings.
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