[PATCH] hysteresis for active cooling

[PATCH] hysteresis for active cooling

[Sanjoy Mahajan]

My laptop's fan was turning on and off as the temperature crossed the
active trip point.  The patch below adds hysteresis: It turns off active
cooling only when the temperature falls, say, 2 C below the trip point.
Maybe the magic difference should be 5 degrees; I'd be curious what
setting suits people best.

Tested and working on my TP 600X (Debian 'etch', kernel 2.6.11.4,
original DSDT with fixes).  It patches cleanly against 2.6.13-rc3 and is
conceptually simple, so I'd hope it works there too.

-Sanjoy

`A society of sheep must in time beget a government of wolves.'
   - Bertrand de Jouvenal


--- linux/drivers/acpi/thermal.c.old	2005-03-17 16:40:04.000000000 -0500
+++ linux/drivers/acpi/thermal.c	2005-07-23 13:44:35.000000000 -0400
@@ -66,6 +66,8 @@
 #define ACPI_THERMAL_MAX_ACTIVE	10
 #define ACPI_THERMAL_MAX_LIMIT_STR_LEN 65
 
+#define AC_HYSTERESIS 2		/* active-cooling hysteresis, in C */
+
 #define KELVIN_TO_CELSIUS(t)    (long)(((long)t-2732>=0) ? ((long)t-2732+5)/10 : ((long)t-2732-5)/10)
 #define CELSIUS_TO_KELVIN(t)	((t+273)*10)
 
@@ -625,8 +627,14 @@
 		 * ----------------
 		 * Turn OFF all cooling devices associated with this
 		 * threshold.
+                 *
+		 * With hysteresis: Turn off only when temp is
+		 * AC_HYSTERESIS [in C] below threshold.  Safer to
+		 * adjust fan-off rather than fan-on behavior.
 		 */
-		else if (active->flags.enabled) {
+		else if (active->flags.enabled &&
+			 KELVIN_TO_CELSIUS(tz->temperature) <=
+			 KELVIN_TO_CELSIUS(active->temperature) - AC_HYSTERESIS) {
 			for (j = 0; j < active->devices.count; j++) {
 				result = acpi_bus_set_power(active->devices.handles[j], ACPI_STATE_D3);
 				if (result) {


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Re: [PATCH] hysteresis for active cooling

[Francisco Figueiredo Jr.]

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Sanjoy Mahajan wrote:
> My laptop's fan was turning on and off as the temperature crossed the
> active trip point.  The patch below adds hysteresis: It turns off active
> cooling only when the temperature falls, say, 2 C below the trip point.
> Maybe the magic difference should be 5 degrees; I'd be curious what
> setting suits people best.
> 


Hi Sanjoy.

How do I know what temperature active cooling will be turned off?

Currently as I type that, my system starts active cooling when it
reaches 52 C and turns off when it reaches 44.


I have the following as my trip_points:

cat /proc/acpi/thermal_zone/THRM/trip_points
critical (S5):           93 C
passive:                 90 C: tc1=2 tc2=3 tsp=100 devices=0xdf6de280
active[0]:               70 C: devices=0xc147de20
active[1]:               60 C: devices=0xc147df40
active[2]:               50 C: devices=0xc147d120

In my system, what your patch would do? Will it turn off fan when it
reach 42, instead of actual 44?

Thanks in advance. And sorry for boring you with these questions. I'm
very interested in fan management in my laptop, since I had a challenge
of knowing how to turn it on and off manually :)



- --
Regards,

Francisco Figueiredo Jr.
Npgsql Lead Developer
http://gborg.postgresql.org/project/npgsql
MonoBrasil Project Founder Member
http://monobrasil.softwarelivre.org


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                  ~ Albert Einstein
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Re: [PATCH] hysteresis for active cooling

[Sanjoy Mahajan]

> Currently as I type that, my system starts active cooling when it
> reaches 52 C and turns off when it reaches 44.

> In my system, what your patch would do? Will it turn off fan when it
> reach 42, instead of actual 44?

I don't know for sure, since I don't understand why your system starts
active cooling at 52 C (instead of 50 C) -- maybe there's hysteresis
in the hardware?  And why does it have to get way down to 44 C instead
of only 50 C before turning off?

>From reading the acpi spec, I understood that the ACPI interpreter is
supposed to handle updating the temperature, querying the embedded
controller, providing interfaces to turn the fan on and off; but that
the OSPM (operating system power management code) is supposed to
decide when to turn the fan on and off.  In Linux that code is in the
thermal module (drivers/acpi/thermal.c), and the only code I found to
turn off active cooling was the else clause of

	    if (tz->temperature >= active->temperature) {

Would an ACPI guru clear up my lack of clue?

-Sanjoy


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Re: [PATCH] hysteresis for active cooling

[Jamie Lentin]

> I don't know for sure, since I don't understand why your system starts
> active cooling at 52 C (instead of 50 C) -- maybe there's hysteresis
> in the hardware?  And why does it have to get way down to 44 C instead
> of only 50 C before turning off?

There is probably hysteresis built into the DSDT.  The ACPI Spec
suggests doing this (don't have a page # handy tho', sorry), it's how
hysteresis is implemented on my laptop (as well as yours---atlhough the
hysteresis code is probably broken as it was on mine.  I'm preparing a
page in the DSDT fixes/rewrites I've done on my laptop, if you're
interested.  Your 600x DSDT code seems pretty much identical to my 770x
code).

Basically, whenever there is a change in fan state, the DSDT can trigger
the OS to re-read the trip-points from the DSDT, and give lower values.
Again, once the fan turns off, it can tell the OS to re-read, and give
higher trip-point values.

The problem with this is I can't really play with my trip-points using
/proc, because as soon as the fan changes state, my changes get
overwritten by the DSDT.  It would be interesting if anyone has any ideas
of getting around this.

Cheers,


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Re: [PATCH] hysteresis for active cooling

[Sanjoy Mahajan]

> The problem with this is I can't really play with my trip-points
> using /proc, because as soon as the fan changes state, my changes
> get overwritten by the DSDT.

Hmm, I've noticed that overwriting when the laptop wakes up from
suspend (S3).  The wakeup script sets the THM2 zone's active trip
point to 50 C, but after maybe 10 or 15 minutes, it reverts to 34C
(the default I think) and the fan turns on -- as it did just a minute
ago.  I haven't noticed this overwriting except after a wakeup;
normally, the setting made using /proc remains constant.  Maybe I
should reload the thermal module upon wakeup, then set the
temperature.

> I'm preparing a page in the DSDT fixes/rewrites I've done on my
> laptop, if you're interested.

Thanks, I'd be interested.  The 600X has the best keyboard of any
computer I've used, even better than my old 560.  With the maximum
memory in it, it is plenty fast enough for what I do (TeX/MetaPost,
computational physics) so I never want to upgrade to a newer and
shoddier piece of hardware, and would like to fix as much as possible
with the 600X's power management.

-Sanjoy


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Re: [PATCH] hysteresis for active cooling

[Francisco Figueiredo Jr.]

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Hash: SHA1

Jamie Lentin wrote:
>>I don't know for sure, since I don't understand why your system starts
>>active cooling at 52 C (instead of 50 C) -- maybe there's hysteresis
>>in the hardware?  And why does it have to get way down to 44 C instead
>>of only 50 C before turning off?
> 
> 
> There is probably hysteresis built into the DSDT.  The ACPI Spec
> suggests doing this (don't have a page # handy tho', sorry), it's how
> hysteresis is implemented on my laptop (as well as yours---atlhough the
> hysteresis code is probably broken as it was on mine.  I'm preparing a
> page in the DSDT fixes/rewrites I've done on my laptop, if you're
> interested.  Your 600x DSDT code seems pretty much identical to my 770x
> code).
> 
> Basically, whenever there is a change in fan state, the DSDT can trigger
> the OS to re-read the trip-points from the DSDT, and give lower values.
> Again, once the fan turns off, it can tell the OS to re-read, and give
> higher trip-point values.
> 

Ahhhh, nice catch!

I never watched my trip points when fan was on.

This is what I get:
cat /proc/acpi/thermal_zone/THRM/trip_points
critical (S5):           93 C
passive:                 90 C: tc1=2 tc2=3 tsp=100 devices=0xdf6de240
active[0]:               70 C: devices=0xc147fe00
active[1]:               60 C: devices=0xc147ff20
active[2]:               45 C: devices=0xc147ffe0

Indeed, my active[2] was changed to 45 C. As I get my fan turned off
when it reaches 42, 41C I think it has the hysteresis already in my dsdt
as Jamie said. This would explain why values when fan is on or off
changes sometimes. I mean, sometimes my fan starts with 51C, other times
with 52C. The same happens when turning off.

Thanks guys for this one more information.



- --
Regards,

Francisco Figueiredo Jr.
Npgsql Lead Developer
http://gborg.postgresql.org/project/npgsql
MonoBrasil Project Founder Member
http://monobrasil.softwarelivre.org


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