linux-kernel - thermal governor: does it actually work??

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Date:	Thu, 14 Feb 2013 16:32:55 +0100
From:	Andreas Mohr <andi@...as.de>
To:	linux-kernel@...r.kernel.org
Cc:	Durgadoss R <durgadoss.r@...el.com>,
	Zhang Rui <rui.zhang@...el.com>, peter@...e.net
Subject: thermal governor: does it actually work??

For me after having loaded acerhdf the fan never stops (with kernelmode
active), despite staying safely below trip point
(acerhdf_set_cur_state() actually never gets called).
And AFAIR in a 3.2.0 kernel acerhdf fan operation seemed to just work
(i.e., no fan for low temps, from the beginning).
Needless to say 3.2.0 didn't even feature all the modern thermal
governor crapyard yet ;)
(ok, well, it's more complex but it's also a very nice environment capability)

3.8-rc7:
CONFIG_ACPI_THERMAL=m
CONFIG_THERMAL=m
CONFIG_THERMAL_HWMON=y
CONFIG_THERMAL_DEFAULT_GOV_STEP_WISE=y
# CONFIG_THERMAL_DEFAULT_GOV_FAIR_SHARE is not set
# CONFIG_THERMAL_DEFAULT_GOV_USER_SPACE is not set
CONFIG_FAIR_SHARE=y
CONFIG_STEP_WISE=y
# CONFIG_USER_SPACE is not set
# CONFIG_CPU_THERMAL is not set

Terminology in this area seems to be quite a bit off, too, at several
docs places, at least according to my understanding:

e.g. drivers/thermal/step_wise.c has the following comment:

/**
 * step_wise_throttle - throttles devices associated with the given zone
 * @tz - thermal_zone_device
 * @trip - the trip point
 * @trip_type - type of the trip point
 *
 * Throttling Logic: This uses the trend of the thermal zone to
 * throttle.
 * If the thermal zone is 'heating up' this throttles all the cooling
 * devices associated with the zone and its particular trip point, by
 * one
 * step. If the zone is 'cooling down' it brings back the performance of
 * the devices by one step.

if ... heating up ... throttles ...
Sorry, but at least for P4 clockmod stuff (or some such), throttle
states (P1...P8 IIRC) meant that the CPU operation was *reduced*,
i.e. with pause intervals.
And the translation of throttle clearly says that it does go that way
and not the other way...
(yes, you managed to confuse me that much that I even had to look up
things to verify)

... cooling down ... brings back ...
This should certainly be worded "reduces" or some such.

So, any idea why I'm missing callbacks in acerhdf (if that is what I'm
supposed to expect to happen)?
Kernel bug, .config mistake, missing/wrong user-side setup?

Needless to say if kernel bug this ought to be fixed pre-3.8 ideally.

Thanks,

Andreas Mohr
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