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Message-ID: <20140217215053.GE7941@thin>
Date: Mon, 17 Feb 2014 13:50:53 -0800
From: Josh Triplett <josh@...htriplett.org>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org,
laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
darren@...art.com, fweisbec@...il.com, oleg@...hat.com, sbw@....edu
Subject: Re: [PATCH tip/core/rcu 1/3] rcu: Optimize rcu_is_nocb_cpu() for
RCU_NOCB_CPU_ALL
On Mon, Feb 17, 2014 at 01:40:25PM -0800, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
>
> If CONFIG_RCU_NOCB_CPU_ALL=y, then rcu_is_nocb_cpu() will always
> return true, however, the current version nevertheless checks
> rcu_nocb_mask. This commit therefore creates a static inline
> implementation of rcu_is_nocb_cpu() that unconditionally returns
> true when CONFIG_RCU_NOCB_CPU_ALL=y.
>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
One suggestion below. With or without that change:
Reviewed-by: Josh Triplett <josh@...htriplett.org>
> include/linux/rcupdate.h | 4 ++++
> kernel/rcu/tree_plugin.h | 2 ++
> 2 files changed, 6 insertions(+)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 72bf3a01a4ee..92365b1fede4 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -1016,7 +1016,11 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
> __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
>
> #ifdef CONFIG_RCU_NOCB_CPU
> +#ifdef CONFIG_RCU_NOCB_CPU_ALL
> +static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
> +#else /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
> bool rcu_is_nocb_cpu(int cpu);
> +#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU_ALL */
> #else
> static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
> #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
This seem clearer if written without the nesting:
#if defined(CONFIG_RCU_NOCB_CPU_ALL)
static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
#elif defined(CONFIG_RCU_NOCB_CPU)
bool rcu_is_nocb_cpu(int cpu);
#else
static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
#endif
That clearly distinguishes the three cases: all, some, none.
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 6e2ef4b2b920..39a50b918bff 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2101,6 +2101,7 @@ static void rcu_init_one_nocb(struct rcu_node *rnp)
> init_waitqueue_head(&rnp->nocb_gp_wq[1]);
> }
>
> +#ifndef CONFIG_RCU_NOCB_CPU_ALL
> /* Is the specified CPU a no-CPUs CPU? */
> bool rcu_is_nocb_cpu(int cpu)
> {
> @@ -2108,6 +2109,7 @@ bool rcu_is_nocb_cpu(int cpu)
> return cpumask_test_cpu(cpu, rcu_nocb_mask);
> return false;
> }
> +#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
>
> /*
> * Enqueue the specified string of rcu_head structures onto the specified
> --
> 1.8.1.5
>
--
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