linux-kernel - Re: [PATCH 4/6] thermal: add sanity check for the passive attribute

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Message-Id: <1251958205.3483.290.camel@rzhang-dt>
Date:	Thu, 03 Sep 2009 14:10:05 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Frans Pop <elendil@...net.nl>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] thermal: add sanity check for the passive attribute

On Mon, 2009-08-31 at 18:30 +0800, Frans Pop wrote:
> On Monday 31 August 2009, Zhang Rui wrote:
> > On Thu, 2009-08-27 at 00:48 +0800, Frans Pop wrote:
> > > On Wednesday 26 August 2009, Matthew Garrett wrote:
> > > > On Wed, Aug 26, 2009 at 06:17:23PM +0200, Frans Pop wrote:
> > > > > Values below 40000 milli-celsius (limit is somewhat arbitrary)
> > > > > don't make sense and can cause the system to go into a thermal
> > > > > heart attack: the actual temperature will always be lower and
> > > > > thus the system will be throttled down to its lowest setting.
> > > >
> > > > Not keen on this - it's a pretty arbitrary cutoff, and there are
> > > > some cases where someone might want this value. Policy belongs in
> > > > userspace, and all that.
> > >
> > > What cases do you see? Testing? Or systems that might have to operate
> > > at such a low temperature? I deliberately chose a value that's at a
> > > level that's easy to reach.
> > >
> > > I agree it is arbitrary, but it will prevent major confusion when
> > > someone like me echo's 95 directly in sysfs.
> >
> > this is a problem.
> > how about something like:
> > #define THERMAL_PASSIVE_WARNING_LEVEL 0x40000
> 
> Hmmm. 40000 hexadecimal? That seems a bit high ;-)
> 
> > if (state < THERMAL_PASSIVE_WARNING_LEVEL)
> >    printk(KERN_WARNING PREFIX "Passive trip point too low, this may"
> >           "slow down your laptop because processors are throttled "
> >           "whenever the temperature is higher than %dC\n", state/1000);
> 
> Disadvantage is that users are unlikely to actually see that message at 
> the time they set the value, especially if they're working in some xterm. 
> They'd have to check dmesg or log files. It also increases the .text size 
> of the module for an option that very few people are likely to use.
> 
> > > Would 1000 (1 °C) perhaps be more acceptable as a limit? I doubt
> > > there are valid use-cases for below 0 temps :-)
> 
> I'd prefer this option. Do you see any downside to this?
> 
I see many laptops with a passive trip point higher than 90C, so a
passive trip point higher than 100C may be meaningful.
I think we should use a higher value, say 2000?

thanks,
rui


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