Date: Mon, 4 Jan 2010 09:31:08 +0100
From: Pavel Machek <pavel@ucw.cz>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: pm list <linux-pm@lists.linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>,
       Linux PCI <linux-pci@vger.kernel.org>,
       ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
       Alan Stern <stern@rowland.harvard.edu>,
       Jesse Barnes <jbarnes@virtuousgeek.org>,
       Matthew Garrett <mjg59@srcf.ucam.org>,
       Oliver Neukum <oliver@neukum.org>, Shaohua Li <shaohua.li@intel.com>,
       Bjorn Helgaas <bjorn.helgaas@hp.com>,
       Francois Romieu <romieu@fr.zoreil.com>, Len Brown <lenb@kernel.org>
Subject: Re: [RFC][PATCH 12/12] PM / r8169: Add simplified run-time PM
	support
Message-ID: <20100104083108.GD1372@ucw.cz>
References: <200911160047.46299.rjw@sisk.pl> <201001022149.05553.rjw@sisk.pl> <20100103195544.GC11928@elf.ucw.cz> <201001032201.14087.rjw@sisk.pl>
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> > > 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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