Mobile/Powersaving
Overview
On mobile devices we want to use the least amount of power, so the device's battery will last as long as possible. Users will likely notice what browsers are better in this and prefer them.
Metrics
- # of wakeups/second, that prevent the CPU from sleeping. See powertop. Relevant in low CPU load.
- Fennec currently has 1.5 wakeups/second when idle.
- CPU %. Relevant in high CPU load.
- Disk usage (tools: iostat, atop).
- Relevant config setting: browser.sessionstore.interval
Ideas
OS-level process control
The 'nuclear option': Use OS-level operations to make processes sleep or use low CPU % when they should. On Linux this can be done with SIG_STOP, SIG_CONT (see e.g. cpulimit).
Uses:
- Put background tabs to sleep (requires one process per tab).
- Force plugins to use low CPU % (Flash etc.)
- Suspend top tab (or all tabs) when panning, or during other certain types of activity.
- Throttle all tabs when battery is low (kind of like laptops dim their monitors on low battery).
- User-controllable speed setting, to save power by throttling?
- Put all tabs to sleep when idle (sort of like a screensaver). Although the mobile OS might already do this to us when it decides the device is idle.
Availability: Probably Meego. Android lacks it in the Java API (but other signals are present, so perhaps it will be added), perhaps using the NDK it is possible though?
Benefits: Straightforward, simple to implement, guarantees the best results.
Status: Working proof of concept on desktop for suspending/freezing the content process as desired.
Firefox-level control
A more messy option: Add separate options throughout our codebase to allow things to be temporarily frozen - JavaScript, animations, plugins, etc. etc.
Tests
- High CPU usage:
- bubblemark
- Hamster dance
- CNN (takes 100% CPU in fennec for no user-apparent reason)