linux-kernel - Re: [PATCH 03/13] rcu: Exclude all potential timekeepers from sysidle detection

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Message-ID: <20131218114633.GR3694@twins.programming.kicks-ass.net>
Date:	Wed, 18 Dec 2013 12:46:33 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Stultz <john.stultz@...aro.org>,
	Alex Shi <alex.shi@...aro.org>,
	Kevin Hilman <khilman@...aro.org>
Subject: Re: [PATCH 03/13] rcu: Exclude all potential timekeepers from
 sysidle detection

On Wed, Dec 18, 2013 at 12:43:18PM +0100, Peter Zijlstra wrote:
> On Wed, Dec 18, 2013 at 12:49:15AM +0100, Frederic Weisbecker wrote:
> > That's to start simple as CPU 0 can't be offlined.
> 
> Yes it can, see CONFIG_BOOTPARAM_HOTPLUG_CPU0

Also, that's a traditional weirdness of x86. Other archs might not have
this constraint at all and can hotplug any cpu.

So relying on the fact that cpu 0 cannot be hotplugged is broken.
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