linux-kernel - Re: [PATCH 2/4 v2] nohz: Split extended quiescent state handling from nohz switch

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Date:	Mon, 6 Jun 2011 16:30:01 -0400
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Russell King <linux@....linux.org.uk>,
	Hans-Christian Egtvedt <hans-christian.egtvedt@...el.com>,
	Mike Frysinger <vapier@...too.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Paul Mackerras <paulus@...ba.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	David Miller <davem@...emloft.net>,
	Guan Xuetao <gxt@...c.pku.edu.cn>
Subject: Re: [PATCH 2/4 v2] nohz: Split extended quiescent state handling
 from nohz switch

On 6/5/2011 11:20 PM, Frederic Weisbecker wrote:
> It is assumed that rcu won't be used once we switch to tickless
> mode and until we restart the tick. However this is not always
> true, as in x86-64 where we dereference the idle notifiers after
> the tick is stopped.
>
> To prepare for fixing this, split the tickless mode switching and
> RCU extended quiescent state logics.
> Make tick_nohz_stop/restart_sched_tick() RCU agnostic but provide
> a new pair of APIs tick_nohz_enter/exit_idle() that keep the
> old behaviour by handling both the nohz mode and RCU extended
> quiescent states, then convert every archs to use these.
>
> Archs that want to switch to extended QS to some custom points
> can do it later by using tick_nohz_stop_sched_tick() and
> rcu_enter_nohz() seperately.
>
> v2: Remove rcu_exit_nohz() from tick_nohz_restart_sched_tick()
>
> [...]
>  arch/tile/kernel/process.c             |    4 +-

Acked-by: Chris Metcalf <cmetcalf@...era.com>

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com


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