linux-kernel - Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical section?

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Date:	Mon, 9 Sep 2013 12:56:06 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...icios.com, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, sbw@....edu
Subject: Re: [PATCH] rcu: Is it safe to enter an RCU read-side critical
 section?

On Fri, Sep 06, 2013 at 10:52:38AM -0700, Paul E. McKenney wrote:
> How about if I made rcu_is_cpu_idle() be as follows?
> 
> int rcu_is_cpu_idle(void)
> {
> 	int ret;
> 
> 	ret = (atomic_read(&per_cpu(rcu_dynticks.dynticks,
> 				    raw_smp_processor_id())) & 0x1) == 0;
> 	return ret;
> }


No, please use __raw_get_cpu_var(), that generates far better code. Also
any such trickery needs a coherent comment.
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