linux-kernel - Re: [linux-pm] [RFC PATCH] thermal: Add support to report cooling statistics achieved by cooling devices

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Date:	Mon, 6 Feb 2012 16:18:18 -0800
From:	Greg KH <greg@...ah.com>
To:	Amit Kachhap <amit.kachhap@...aro.org>
Cc:	Pavel Machek <pavel@....cz>, linux-pm@...ts.linux-foundation.org,
	linaro-dev@...ts.linaro.org, patches@...aro.org,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	rob.lee@...aro.org
Subject: Re: [linux-pm] [RFC PATCH] thermal: Add support to report cooling
 statistics achieved by cooling devices

On Mon, Feb 06, 2012 at 03:16:17PM -0800, Amit Kachhap wrote:
> On 6 February 2012 09:03, Greg KH <greg@...ah.com> wrote:
> > On Mon, Feb 06, 2012 at 05:56:58PM +0100, Pavel Machek wrote:
> >> Hi!
> >>
> >> > Add a sysfs node code to report effective cooling of all cooling devices
> >> > attached to each trip points of a thermal zone. The cooling data reported
> >> > will be absolute if the higher temperature trip points are arranged first
> >> > otherwise the cooling stats is the cumulative effect of the earlier
> >> > invoked cooling handlers.
> >> >
> >> > The basic assumption is that cooling devices will bring down the temperature
> >> > in a symmetric manner and those statistics can be stored back and used for
> >> > further tuning of the system.
> >>
> >> /sys fs should be one-value-per-file, talk to gregkh.
> >
> > That's correct.
> >
> > Why not use debugfs for this instead?
> >
> > thanks,
> >
> > greg k-h
> 
> Thanks Greg/Pavel for looking into the patch.
> Basically I checked the places where single sysfs entry is showing
> more then 1 output. And
> 1) /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state
> 2) /sys/devices/system/cpu/cpu0/cpufreq/stats/trans_table
> are the places where the output is more than 1 value.

Yes, those are two known-bad files, whose files will change soon and
move to debugfs.

Just because you found 2, instead of the thousands of other properly
formatted files, does not mean you are allowed to create something like
this.

> Anyway I can enclose this sysfs inside CONFIG_THERMAL_COOLING_STATS macro.

No, you can not create it at all in sysfs, if you really need such a
large single file, use debugfs instead, that is what it is there for.

Again, one-value-per-file is the sysfs rule, and has been for a decade
now, please don't think this is a new thing.

greg k-h
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