linux-kernel - Re: Power Saving

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Message-ID: <474C9AC9.8000400@cfl.rr.com>
Date:	Tue, 27 Nov 2007 17:31:37 -0500
From:	Phillip Susi <psusi@....rr.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Dave Jones <davej@...hat.com>,
	Stephen Clark <Stephen.Clark@...lark.us>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Power Saving

H. Peter Anvin wrote:
> And more importantly, there is no power advantages over T states as 
> opposed to C states.  They pretty much mean pulsing the system in and 
> out of either C1 or C2 depending on the CPU/chipset.

Well, they FORCE the use of the C states to save power, even if the 
kernel doesn't want to because it still has runnable tasks.  This can be 
useful if you know you are running a task that busy waits but would not 
suffer from having the performance of the cpu cut in half.  Since it is 
busy waiting, the kernel never activates the C states, but the 
throttling will force it and thus, save you power and heat.

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