linux-kernel - Re: 2.6.22 regression: thermal trip points

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Message-ID: <20070806095504.GA1934@elf.ucw.cz>
Date:	Mon, 6 Aug 2007 11:55:04 +0200
From:	Pavel Machek <pavel@....cz>
To:	Len Brown <lenb@...nel.org>
Cc:	trenn@...e.de, Andi Kleen <andi@...stfloor.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Knut Petersen <Knut_Petersen@...nline.de>,
	linux-kernel@...r.kernel.org, mjg59@...f.ucam.org
Subject: Re: 2.6.22 regression: thermal trip points

Hi!

> > If we have something like this, we could still discuss a config option,
> > that also allows to increase trip points, marking it with "If you set
> > this you can destroy your machine, you have been warned...". While this
> > would not be an option for distributions to compile in, some people may
> > come around the biggest hammer -> overriding DSDT.
> > 
> > I cannot promise, but I try to get this for 2.6.24.
> 
> I think if you are enamored with overriding trip points at SuSE,
> that you should simply restore the original scheme as the "value add"
> for SuSE kernels.  Seriously, I'm totally fine with that.
> 
> You should be aware, however, that (one of) the fundamental flaws
> with that scheme, shared with what you describe above, is that the OS
> can not actually change the trip points in the thermal sensor.
> The sensor is going to trip at the temperature that _it_ thinks

Yep, you work around this one by enabling polling.

> This faking out the user, plus the fact that the BIOS does change
> trip-points at run-time, made the original scheme fundamentally
> unsound.  Further, I've not yet found a single system where use

Yes, this one is uglier. But maybe "enable polling automatically +
ignore any updates from bios" (+ maybe "only enable lowering") is
better solution than "just remove the knob"? After all, "the knob" is
still useful for debugging at least.

> of this scheme wasn't papering over some other problem.  For the
> upstream kernel, I think it is more appropriate to expose and fix
> the fundamental problems.  For distro kernels, I'm less concerned
> if you hide bugs instead of fixing them.

This is okay as long as you are willing to work around the fundamental
problems in kernel. You are unable to _fix_ them. They are broken
BIOSes.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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