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

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Message-ID: <20121114013459.GS2489@linux.vnet.ibm.com>
Date:	Tue, 13 Nov 2012 17:34:59 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:	Arjan van de Ven <arjan@...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

On Tue, Nov 13, 2012 at 05:14:50PM -0800, Jacob Pan wrote:
> On Tue, 13 Nov 2012 16:08:54 -0800
> Arjan van de Ven <arjan@...ux.intel.com> wrote:
> 
> > > 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)

Another round of RCU_FAST_NO_HZ rework, you are asking for?  ;-)

> Another reason is my observation that there are some assumptions/checks
> to make sure only idle thread can tell rcu it is idle. Is it ok to
> extend that to other kthreads?

If you are only having the system take 6-millisecond "vacations", probably
best to try it as it is and fix specific problems if/when they arise.

							Thanx, Paul

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