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

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Date:	Sun, 05 Jun 2011 20:58:23 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	fweisbec@...il.com
Cc:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	mingo@...e.hu, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	hpa@...or.com, linux@....linux.org.uk,
	hans-christian.egtvedt@...el.com, vapier@...too.org,
	ralf@...ux-mips.org, paulus@...ba.org, heiko.carstens@...ibm.com,
	lethal@...ux-sh.org, cmetcalf@...era.com, gxt@...c.pku.edu.cn
Subject: Re: [PATCH 2/4] nohz: Split extended quiescent state handling from
 nohz switch

From: Frederic Weisbecker <fweisbec@...il.com>
Date: Mon,  6 Jun 2011 05:10:56 +0200

> 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.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>

Acked-by: David S. Miller <davem@...emloft.net>
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