linux-kernel - Re: [PATCH 3/3] PM: Introduce Intel PowerClamp Driver

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Date:	Tue, 13 Nov 2012 16:08:54 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Linux PM <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Len Brown <len.brown@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Zhang Rui <rui.zhang@...el.com>, Rob Landley <rob@...dley.net>
Subject: Re: [PATCH 3/3] PM: Introduce Intel PowerClamp Driver


> 
> OK, so the point of clamping all sockets simultaneously is to be able
> to power down the electronics surrounding the sockets as well as the
> sockets themselves?  

yup; memory can go to self refresh etc etc

>If all you cared about was the individual sockets,
> I don't see why you couldn't power the sockets down individually rather
> than in sync with each other.

the hardware that this driver supports does not support powering down sockets individually.

(since the memory controllers are part of the "socket"... it would increase latency
etc etc, and likely wreak havoc with the cache coherency protocols)

> I think I know, but I feel the need to ask anyway.  Why not tell
> RCU about the clamping?

I don't mind telling RCU, but what cannot happen is a bunch of CPU time suddenly getting used
(since that is the opposite of what is needed at the specific point in time of going idle)

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