linux-kernel - Re: [PATCH tip/core/rcu 05/15] rcu: Move _rcu_barrier()'s rcu_head structures to rcu

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Date:	Fri, 15 Jun 2012 15:19:16 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 05/15] rcu: Move _rcu_barrier()'s rcu_head
 structures to rcu_data structures

On Fri, Jun 15, 2012 at 02:06:00PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> 
> In order for multiple flavors of RCU to each concurrently run one
> rcu_barrier(), each flavor needs its own per-CPU set of rcu_head
> structures.  This commit therefore moves _rcu_barrier()'s set of
> per-CPU rcu_head structures from per-CPU variables to the existing
> per-CPU and per-RCU-flavor rcu_data structures.
> 
> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

Reviewed-by: Josh Triplett <josh@...htriplett.org>

>  kernel/rcutree.c |    6 ++----
>  kernel/rcutree.h |    3 +++
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 8b3ab4e..2cfbdb8 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -157,7 +157,6 @@ unsigned long rcutorture_vernum;
>  
>  /* State information for rcu_barrier() and friends. */
>  
> -static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
>  static atomic_t rcu_barrier_cpu_count;
>  static DEFINE_MUTEX(rcu_barrier_mutex);
>  static struct completion rcu_barrier_completion;
> @@ -2279,12 +2278,11 @@ static void rcu_barrier_callback(struct rcu_head *notused)
>   */
>  static void rcu_barrier_func(void *type)
>  {
> -	int cpu = smp_processor_id();
> -	struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
>  	struct rcu_state *rsp = type;
> +	struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
>  
>  	atomic_inc(&rcu_barrier_cpu_count);
> -	rsp->call(head, rcu_barrier_callback);
> +	rsp->call(&rdp->barrier_head, rcu_barrier_callback);
>  }
>  
>  /*
> diff --git a/kernel/rcutree.h b/kernel/rcutree.h
> index 15837d7..1783eae 100644
> --- a/kernel/rcutree.h
> +++ b/kernel/rcutree.h
> @@ -300,6 +300,9 @@ struct rcu_data {
>  	unsigned long n_rp_need_fqs;
>  	unsigned long n_rp_need_nothing;
>  
> +	/* 6) _rcu_barrier() callback. */
> +	struct rcu_head barrier_head;
> +
>  	int cpu;
>  	struct rcu_state *rsp;
>  };
> -- 
> 1.7.8
> 
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