From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Pavel Machek <pavel@ucw.cz>
Subject: Re: [RFC][PATCH 12/12] PM / r8169: Add simplified run-time PM support
Date: Mon, 4 Jan 2010 20:51:08 +0100
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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>
References: <200911160047.46299.rjw@sisk.pl> <201001032201.14087.rjw@sisk.pl> <20100104083108.GD1372@ucw.cz>
In-Reply-To: <20100104083108.GD1372@ucw.cz>
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On Monday 04 January 2010, Pavel Machek wrote:
> 
> > > > 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.

But still energy is what you pay for, isn't it?

> You are right that on notebooks, energy is more important.)

You may require less power to run, so if that's what you mean by "saving", then
I agree. :-)

Rafael
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