Re: passive cooling policy

[Dominik Brodowski <linux-X3ehHDuj6sIIGcDfoQAp7BvVK+yQ3ZXh@public.gmane.org>]

Hi Thomas,

> 3) If passive limit is reached, kernel throttles cpu and tries to set 
> cpufreq to lowest step. Only way to find out whether machine is 
> passively cooled is in polling /proc/acpi/thermal_zone/*/state.
> (Is it right that cpufreq daemons poll this file to be informed of 
> kernel forced cpufreq slow downs?)

Why do cpufreq daemons want to know that? And the ordering is important:
first scale CPU frequency be means of cpufreq, _then_ throttle the CPU.

> 1) inform userspace that cpu speed is increased/decreased through a 
> thermal event.
> -> avoid userspace progs polling /proc/acpi/thermal_zone/*/state to be 
> informed whether the system is slowed down.

Again, I do not see a reason for why this needs to be exported to userspace.

> 2) Allow setting a passive trip point even BIOS does not export a 
> passive trip point value and initialise tc1, tc2 and tsp with some 
> sensible default values.
> -> you could lower fan activity on every laptop/workstation that 
> supports throttling/cpufreq regardless whether the BIOS exports any 
> passive trip points/cooling mode (event most laptop vendors don't care 
> about trip points).

As long as this allows an additional, probably lower "trip point" for
_passive_ cooling, this sounds like a good idea. It cannot hurt as long as
it doesn't disable the BIOS-initialized active cooling.

	Dominik


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