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

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Message-ID: <p73odlzkb6h.fsf@bingen.suse.de>
Date:	08 Apr 2007 01:38:14 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Andika Triwidada" <andika@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: CPU offline but power consumption increased?

"Andika Triwidada" <andika@...il.com> writes:

[cc linux-acpi]

> Question: is that normal? I thought power consumption will be
> automatically reduced if one core offlined.

The current cpu offline essentially just runs a special idle loop.
The standard idle loop is even a bit more aggressive on some systems
because it knows about the deeper ACPI sleep modi.

There are also dependencies between cores because current CPUs
have shared power planes between cores.

I suppose in the future when a whole socket goes off line one could
implement special code to turn off the CPU further. But it likely
won't work on older hardware.

-Andi
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