Prefs presets

A proposal for simplifying the prefs interface by providing a few "presets" - named preference sets - as the default interface.

Note: another design doc proposes more sweeping changes. This doc doesn't propose changing the preferences, just the interface.

Initially this would be in the web interface. Eventually the Manager should provide the same interface.

Proposed presets

(TODO: fill in the actually preferences for each of the following)

Max computing

Allow computing on all CPUs and GPUs, all the time. Fan noise and power usage not issues.

Standard

Be inaudible and invisible (in particular, don't cause fans to go on high speed). Given that, compute as much as possible.

To implement this properly we need detection of fan speeds (system, CPU, GPU).

Need to not run VMs while busy (or maybe keep 1 core free), until VBox fixes priority issue.

Energy-saver

Compute as energy-efficiently as possible.

To implement this properly we need to look at Peter Hannape's work and figure out how to put the CPU into the mode that maximizes FLOPS/watt.

Don't compute while idle; let the computer go into low-power mode or turn off

Implementation

If a user selects one of these, we should store the preset name (max, standard, green) in user.global_prefs, rather than the prefs themselves. The scheduler can send the corresponding prefs in its reply. This will let us change/extend the meanings of the presets.

Users can still edit any pref. But if they change anything, they're not using the preset anymore.