Energy

How much energy an app uses over a stretch of time, while you use it.

emulabzip energy com.example.app --seconds 30
emulabzip energy com.example.app --json

Start it, use the app, and it reads the result when the time is up, or when you press Ctrl+C.

Android#

The device is unplugged in the battery service's eyes (dumpsys battery unplug) and the statistics are reset (dumpsys batterystats --reset), so that they are counted on the device. At the end dumpsys batterystats --charged <package> is read for the app's uid, and the battery is put back (dumpsys battery reset) always, also after an error or Ctrl+C.

The report has:

• the system's estimated use in mAh, and the parts it comes from (CPU, radio, screen, sensors…);
• the processor time the app used;
• wake locks (how long each was held and how many times), alarms and jobs;
• the network bytes received and sent.

An emulator has no battery. Android computes these numbers from a power model, so compare one run with another run, not with a phone. An app that used too little in the time, or that was not running, gets no estimate, and the report says so.

iOS Simulator#

The simulator has no power model, so there is no figure in mAh. The report gives the CPU time the app used (what drains a real battery first) and the Mac's thermal state (pmset -g therm): when the Mac slows its processor down, two runs are not comparable.

Where to find it#

• Desktop: Performance → Energy (Start, then Stop and read).
• CLI: emulabzip energy.
• MCP: measure_energy (at most 120 seconds).