linux-kernel - Re: How to document dimension units for virtual files?

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Message-Id: <0DFC5218-DA70-42BA-9CCA-C9CA761F8B72@mac.com>
Date:	Sun, 12 Nov 2006 23:33:52 -0500
From:	Kyle Moffett <mrmacman_g4@....com>
To:	Sanjoy Mahajan <sanjoy@...o.cam.ac.uk>
Cc:	Pavel Machek <pavel@....cz>, Michael Holzheu <holzheu@...ibm.com>,
	Ingo Oeser <ioe-lkml@...eria.de>, linux-kernel@...r.kernel.org,
	mschwid2@...ibm.com
Subject: Re: How to document dimension units for virtual files?

On Nov 10, 2006, at 10:41:09, Sanjoy Mahajan wrote:
>> Watts are an indication of power emitted or consumed per unit time  
>> (as opposed to current/amperage which counts only the number of  
>> electrons and not the change in energy), so perhaps  
>> "power_flow:mW" or "power_consumption:mW" would make more sense?
>
> So all of the following make sense:
>
> * "Power:mW"
> * "energy flow: mW" (more verbose but equivalent)
> * "energy flow: mJ/s" (even more verbose but also equivalent)

In this case the name is a sysfs file to indicate the load on the  
battery; so spaces are frowned upon and "load:mW" would probably work  
the best.

>> I can conceivably see a need for a "current:mJ_per_s" versus  
>> "current:mW" depending on the hardware-reported units, but never  
>> both at the same time.
>
> I got lost here.  mJ/s is the same as mW, so with either current:mW  
> or current:mJ/s you're back in the soup of measuring current using  
> units of power

Whoops; sorry, I was writing this too early in the morning without my  
caffeine and got myself turned around.  What I _meant_ to say was this:

"I conceivably see a need for a "load:mC_s" versus "load:mW",  
depending on the hardware-reported units, but never both at the same  
time."

Essentially if the hardware reports units of milli-watts or milli- 
Calories-per-second or whatever, then we should report that directly  
and let userspace convert as appropriate; keeping the floating-point  
out of the kernel.

Cheers,
Kyle Moffett

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