linux-kernel - Re: CPU offline but power consumption increased?

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Message-ID: <20070410134458.GA723@one.firstfloor.org>
Date:	Tue, 10 Apr 2007 15:44:58 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Len Brown <lenb@...nel.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Andika Triwidada <andika@...il.com>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: CPU offline but power consumption increased?

> Speaking for all Intel hardware implemented from pre-history until now,
> deep C-states is the best you can do, and there is no special offline
> mode to save more power.

We don't use deep c states currently; just HLT.

Right now it doesn't make much difference because no multi socket
servers do deep C states and secondary cores can normally not go
deep on their own; but if any of this changes this code would
need to be fixed.

But cpu off line is really a special case -- maybe it is even 
possible to do something better on current hardware.

> and if the BIOS is implemented properly, the core will be spinning in the
> deepest available C-state.  Of course, it would probably be more interesting
> to simply leave the core on-line and let it go idle...

I don't see any BIOS call in play_dead()

-Andi

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