linux-kernel - Re: [PATCH v2 1/2] sched: Add cond_resched_rcu

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Date:	Fri, 3 May 2013 20:09:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Julian Anastasov <ja@....bg>, Simon Horman <horms@...ge.net.au>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Ingo Molnar <mingo@...hat.com>, lvs-devel@...r.kernel.org,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Dipankar Sarma <dipankar@...ibm.com>
Subject: Re: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper

> This happens in only two cases:
> 
> 1.	CONFIG_PREEMPT_RCU=n kernels.  But in this case, rcu_read_unlock()
> 	and rcu_read_lock() are free, at least for CONFIG_PROVE_LOCKING=n
> 	kernels.  And if you have CONFIG_PROVE_LOCKING=y, any contribution
> 	from rcu_read_unlock() and rcu_read_lock() will be in the noise.

Oh argh.. I completely overlooked that rcu_read_{,un}lock() are NOPs for
PREEMPT=n kernels.

/me crawls back under his stone..
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