Re: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper

To: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper
Cc: Julian Anastasov <ja@xxxxxx>, Simon Horman <horms@xxxxxxxxxxxx>, Eric Dumazet <eric.dumazet@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, lvs-devel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>, Dipankar Sarma <dipankar@xxxxxxxxxx>
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Fri, 3 May 2013 20:09:26 +0200
> 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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