linux-kernel - Re: [RFC][PATCH 12/12] PM / r8169: Add simplified run-time PM support

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Message-ID: <20100104083108.GD1372@ucw.cz>
Date:	Mon, 4 Jan 2010 09:31:08 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Oliver Neukum <oliver@...kum.org>,
	Shaohua Li <shaohua.li@...el.com>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Francois Romieu <romieu@...zoreil.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFC][PATCH 12/12] PM / r8169: Add simplified run-time PM
	support


> > > Using /proc/acpi/battery/BAT1/state I measured the energy drawn in 10 minutes
> > > both with the network adapter in D0 and D3hot.  The results were that with the
> > > network adapter in D0 the box drew 2476 mWh, while with the network adapter in
> > > D3hot it drew 2361 mWh.  The difference is 115 mWh, or about 5% on this
> > > particular box.
> > > 
> > > This means about 0.1 Wh in 10 minutes, so we can save about 0.6 Wh per hour.
> > 
> > Which means it saves 0.6W :-). Measuring power in Wh/h is "interesting".
> 
> You can't save power, you can only save energy.  Wh is just an energy unit.

Of course we can save power, you just did :-).

(And in some cases -- data centers, limited cooling -- you are limited
by power, not energy. You are right that on notebooks, energy is more
important.)


									Pavel

-- 
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