linux-kernel - Re: [PATCH v5 tip/core/rcu 15/16] rcu: Make RCU-tasks wait for idle tasks

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Message-ID: <20140813182528.GF4752@linux.vnet.ibm.com>
Date:	Wed, 13 Aug 2014 11:25:28 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, dhowells@...hat.com,
	edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com,
	oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH v5 tip/core/rcu 15/16] rcu: Make RCU-tasks wait for idle
 tasks

On Wed, Aug 13, 2014 at 06:35:22PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 13, 2014 at 07:43:32AM -0700, Paul E. McKenney wrote:
> > So the first three look OK to hook rcu_idle_enter() and rcu_idle_exit()
> > into, but the last two don't look so good.
> > 
> > That said, if you are OK not tracing the stuff under stop_critical_timings(),
> > then I can use the RCU dyntick-idle state and not wake anything up.
> 
> Either way, Steve could easily whip up a debug thing that could validate
> that. Simply WARN whenever an __mcount happens when under rcu_idle.
> 
> And if we make these idle functions small enough that should not be a
> problem at all.

Right now, the CPU-idle drivers look quite hairy and error-prone.

							Thanx, Paul

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