linux-kernel - Re: [PATCH RFC idle 1/3] x86: Avoid invoking RCU when CPU is idle

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Date:	Wed, 1 Feb 2012 20:55:38 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"H. Peter Anvin" <hpa@...or.com>, Len Brown <lenb@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Stephen Wilson <wilsons@...rt.ca>, linux-pm@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH RFC idle 1/3] x86: Avoid invoking RCU when CPU is idle

On Thu, Feb 02, 2012 at 02:54:30AM +0100, Frederic Weisbecker wrote:
> On Wed, Feb 01, 2012 at 04:43:22PM -0800, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> > 
> > The idle loop is a quiscent state for RCU, which means that RCU ignores
> > CPUs that have told RCU that they are idle via rcu_idle_enter().  There
> > are nevertheless quite a few places where idle CPUs use RCU, most commonly
> > indirectly via tracing.  This patch fixes these problems for x86.
> > 
> > Many of these bugs have been in the kernel for quite some time, but
> > Frederic's recent change now gives warnings.
> > 
> > This patch takes the straightforward approach of pushing the
> > rcu_idle_enter()/rcu_idle_exit() pair further down into the core
> > of the idle loop.
> 
> I guess this is about the trace_power_*() things, right?

Indeed it is!  Alternative suggestions gladly accepted.  ;-)

							Thanx, Paul

> Acked-by: Frederic Weisbecker <fweisbec@...il.com>
> 
> Thanks.
> 

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