Automatically enter Battery Life when battery is low about system76-power

[ayoungethan]

I am not sure I agree with this setting, but I am still trying to understand the parameters that each setting modifies.

Perhaps an automatic screen dim or other performance tuning, but the CPU tuning does not itself necessarily lead to more effective battery usage. For example, on my system, I notice in "battery life" mode via powertop that baseline computer power usage increases, which appears due to the computer entering into deeper c-states less frequently, and staying there for shorter periods of time, which means higher baseline power usage, as well as lower maximum power usage, but longer periods of time at the max power state.

This resembles older debates about "ondemand" vs "conservative" CPU frequency scaling governor settings, where people found that "ondemand" actually gave better performance AND battery life in MOST use cases. In the new Intel pstates governor, even the "performance" governor is supposed to allow for power saving equal to the old "ondemand" acpi governor.

This to me begs the question of whether "battery life" should include any CPU tuning at all. Simply downclocking the CPU does not necessarily lead to an intended outcome of reduced power consumption. If we keep CPU tuning, then maybe renaming it to something like "conservative" would make sense. But perhaps it makes more sense just to have two settings: performance and powersave (mirroring or using the pstate governors as baselines, with additional system tweaks).

In my case, I am dealing with low latency audio processing. "battery life" only provides better battery life when doing dynamic open-ended (vs finite) CPU-intensive tasks (such as playing a virtual instrument), by limiting the overall CPU power available. It does NOT necessarily provide better battery life in standard use scenarios, including finite CPU-intensive tasks with well-defined completion parameters (such as transcoding an audio file), because it makes the processor work longer before it re-enters an idle sleep state. However, because it limits overall frequency shifts, it also provides better thermal management. The system can run cooler and thus the fan will operate with less frequency and intensity, which is optimal for situations where fan noise is an issue. It also extends battery life in situations that tend to use all available processing power.

For my case, both "battery life" and "performance" settings are better for a stable low latency audio processing setup, as they decrease the amount of frequency scaling and thus reduce overall latency and jitter. "Balanced" causes far more xruns precisely because it more readily switches between minimum and maximum performance modes, which maximizes latency overheads and adds significant jitter to the signal latency.