linux-kernel - Re: [PATCH 1/2] hwmon: Enhance the sysfs API for power meters.

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Message-ID: <20090808214830.GC24153@elf.ucw.cz>
Date:	Sat, 8 Aug 2009 23:48:30 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	Len Brown <lenb@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	lm-sensors <lm-sensors@...sensors.org>,
	linux-acpi <linux-acpi@...r.kernel.org>,
	Zhang Rui <rui.zhang@...el.com>
Subject: Re: [PATCH 1/2] hwmon: Enhance the sysfs API for power meters.

On Sat 2009-08-08 10:40:20, Darrick J. Wong wrote:
> On Fri, Aug 07, 2009 at 08:09:06PM +0200, Pavel Machek wrote:
> > 
> > > @@ -365,6 +373,16 @@ power[1-*]_average_lowest	Historical average minimum power use
> > >  				Unit: microWatt
> > >  				RO
> > >  
> > > +power[1-*]_average_max		A notification is sent when power use
> > > +				rises above this value.
> > > +				Unit: microWatt
> > > +				RW
> > > +
> > 
> > How is the notification sent?
> 
> ACPI Notify is sent to the kernel, which passes it to the ACPI
> netlink socket.

Uhuh. This is hwmon documentation AFAICT; so a) it should be
documented here, and b) interface should be generic so that it works
without ACPI, too.

> > > +power[1-*]_average_min		A notification is sent when power use
> > > +				sinks below this value.
> > > +				Unit: microWatt
> > > +				RW
> > 
> > And what is this good for? Will it wake from sleep? Will it wake from
> > C3?
> 
> All it really does is generates an ACPI Notify event, which is a hint to the OS
> that it could re-read the power meter use.

So it is one-shot? Document that.

> > ...seems like good way to prevent deep sleep states.
> > 
> > > +power[1-*]_cap			If power use rises above this limit, the
> > > +				system should take action to reduce
> > > power use.
> > 
> > System as in 'hw'? Or who? And how?
> 
> The ACPI spec is silent on this matter.  It's not clear if the OS is supposed
> to monitor and take action on its own when power > cap, or if the hardware/BIOS
> will take action, or possibly both...?

Having user<->kernel interface that is well... uh... undocumented
makes little sense.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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