linux-kernel - Re: Attempted summary of suspend-blockers LKML thread, take three

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Message-ID: <20100815070004.GD2461@linux.vnet.ibm.com>
Date:	Sun, 15 Aug 2010 00:00:04 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Pavel Machek <pavel@....cz>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Felipe Contreras <felipe.contreras@...il.com>,
	"Ted Ts'o" <tytso@....edu>, david@...g.hm,
	Brian Swetland <swetland@...gle.com>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	arve@...roid.com, mjg59@...f.ucam.org, florian@...kler.org,
	rjw@...k.pl, stern@...land.harvard.edu, peterz@...radead.org,
	tglx@...utronix.de, menage@...gle.com, david-b@...bell.net,
	James.Bottomley@...e.de, swmike@....pp.se, galibert@...ox.com,
	dipankar@...ibm.com
Subject: Re: Attempted summary of suspend-blockers LKML thread, take three

On Sat, Aug 14, 2010 at 09:53:51AM -0700, Arjan van de Ven wrote:
> On Sat, 14 Aug 2010 08:10:48 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > 
> > So once you are down to one CPU, the last CPU shuts the system off,
> > itself included?  Or does the last CPU "run" in a deep idle state
> > throughout suspend?  (My guess is the former, and I am also curious
> > whether the cache SRAMs are powered off, etc.  But figured I should
> > ask rather than guessing.)
> 
> they tend to go "off".
> 
> however I think you're making an assumption that there is a
> real difference between a deep idle state and "off"....
> 
> For modern x86 hardware, that assumption isn't really valid.
> (other than a very very small sram that stores register content in the
> idle case)

I am and have been taking you at your word that some systems can reach
power levels while idle that rival suspended/off.  The differences between
idle and suspend are instead semantic, have been posted here more than
once, and make themselves felt when the non-suspended system is non-idle,
even for systems whose deep-idle power approximates that of suspend/off.

							Thanx, Paul
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