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

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Date:	Mon, 4 Jan 2010 20:51:08 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
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

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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