Date:	Fri, 15 Feb 2013 09:47:07 +0000
From:	"Zhang, Rui" <rui.zhang@...el.com>
To:	Andreas Mohr <andi@...as.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"R, Durgadoss" <durgadoss.r@...el.com>,
	"peter@...e.net" <peter@...e.net>,
	"lenb@...nel.org" <lenb@...nel.org>
Subject: RE: thermal governor: does it actually work??



> -----Original Message-----
> From: Andreas Mohr [mailto:andi@...as.de]
> Sent: Thursday, February 14, 2013 11:33 PM
> To: linux-kernel@...r.kernel.org
> Cc: R, Durgadoss; Zhang, Rui; peter@...e.net
> Subject: thermal governor: does it actually work??
> Importance: High
> 
> 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).

Please attach the output of
"grep . /sys/class/thermal/thermal_zone*/cdev*/*"?

> 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.

For processors, surely you are right.

> 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)
> 

The question is that if we can also call it "throttle" when reducing the device performance to generate less heat.

I do not have a clear answer for this as I'm not a native English speaker.
And what you're saying here may be right.
Surely I can generate a patch to rename it if throttle can't be used in that way.

Len,
What's your idea on this?

Thanks,
rui
> ... 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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