Message-ID: <474C9AC9.8000400@cfl.rr.com>
Date: Tue, 27 Nov 2007 17:31:37 -0500
From: Phillip Susi <psusi@cfl.rr.com>
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To: "H. Peter Anvin" <hpa@zytor.com>
CC: Dave Jones <davej@redhat.com>, Stephen Clark <Stephen.Clark@seclark.us>,
       linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: Power Saving
References: <47422D3B.8080704@seclark.us> <20071120005443.GB9243@redhat.com> <474232D9.20407@seclark.us> <20071120011236.GA17420@redhat.com> <474236A0.8030601@zytor.com>
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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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