linux-kernel - Re: suspend blockers & Android integration

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Date:	Thu, 3 Jun 2010 20:45:21 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, tytso@....edu,
	Brian Swetland <swetland@...gle.com>,
	Neil Brown <neilb@...e.de>, Arve Hj?nnev?g <arve@...roid.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Bottomley <James.Bottomley@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Kevin Hilman <khilman@...prootsystems.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: suspend blockers & Android integration

On Thu, 3 Jun 2010 19:26:50 -0700 (PDT)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 
> If the system is idle (or almost idle) for long times, I would
> heartily recommend actively shutting down unused cores. Some CPU's
> are hopefully smart enough to not even need that kind of software
> management, but I suspect even the really smart ones might be able to
> take advantage of the kernel saying: "I'm shutting you down, you
> don't have to worry about latency AT ALL, because I'm keeping another
> CPU active to do any real work".

sadly the reality is that "offline" is actually the same as "deepest C
state". At best.

As far as I can see, this is at least true for all Intel and AMD cpus.

And because there's then no power saving (but a performance cost), it's
actually a negative for battery life/total energy.

(lots of experiments inside Intel seem to confirm that, it's not just
theory)





-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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