Re: [PATCH tip/core/rcu 2/3] rcu: Optimize rcu_needs_cpu() for RCU_NOCB_CPU_ALL

[Josh Triplett <josh@joshtriplett.org>]

On Mon, Feb 17, 2014 at 01:40:26PM -0800, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> 
> If CONFIG_RCU_NOCB_CPU_ALL=y, then rcu_needs_cpu() will always
> return false, however, the current version nevertheless checks
> for RCU callbacks.  This commit therefore creates a static inline
> implementation of rcu_needs_cpu() that unconditionally returns false
> when CONFIG_RCU_NOCB_CPU_ALL=y.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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

> ---
>  include/linux/rcupdate.h | 9 +++++++++
>  include/linux/rcutiny.h  | 6 ------
>  include/linux/rcutree.h  | 2 ++
>  kernel/rcu/tree.c        | 2 +-
>  kernel/rcu/tree_plugin.h | 4 ++++
>  5 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 92365b1fede4..da77ef26b4ac 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -1015,6 +1015,15 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
>  #define kfree_rcu(ptr, rcu_head)					\
>  	__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
>  
> +#if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL)
> +
> +static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
> +{
> +	*delta_jiffies = ULONG_MAX;
> +	return 0;
> +}
> +#endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */
> +
>  #ifdef CONFIG_RCU_NOCB_CPU
>  #ifdef CONFIG_RCU_NOCB_CPU_ALL
>  static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 6f01771b571c..9524903487d0 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -68,12 +68,6 @@ static inline void kfree_call_rcu(struct rcu_head *head,
>  	call_rcu(head, func);
>  }
>  
> -static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
> -{
> -	*delta_jiffies = ULONG_MAX;
> -	return 0;
> -}
> -
>  static inline void rcu_note_context_switch(int cpu)
>  {
>  	rcu_sched_qs(cpu);
> diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
> index 72137ee8c603..81198c84e268 100644
> --- a/include/linux/rcutree.h
> +++ b/include/linux/rcutree.h
> @@ -31,7 +31,9 @@
>  #define __LINUX_RCUTREE_H
>  
>  void rcu_note_context_switch(int cpu);
> +#ifndef CONFIG_RCU_NOCB_CPU_ALL
>  int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies);
> +#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
>  void rcu_cpu_stall_reset(void);
>  
>  /*
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index b3d116cd072d..c2c8234a0291 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2880,7 +2880,7 @@ static int rcu_pending(int cpu)
>   * non-NULL, store an indication of whether all callbacks are lazy.
>   * (If there are no callbacks, all of them are deemed to be lazy.)
>   */
> -static int rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
> +static int __maybe_unused rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
>  {
>  	bool al = true;
>  	bool hc = false;
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 39a50b918bff..820b06aefbee 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1586,11 +1586,13 @@ static void rcu_prepare_kthreads(int cpu)
>   * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
>   * any flavor of RCU.
>   */
> +#ifndef CONFIG_RCU_NOCB_CPU_ALL
>  int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
>  {
>  	*delta_jiffies = ULONG_MAX;
>  	return rcu_cpu_has_callbacks(cpu, NULL);
>  }
> +#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
>  
>  /*
>   * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
> @@ -1696,6 +1698,7 @@ static bool rcu_try_advance_all_cbs(void)
>   *
>   * The caller must have disabled interrupts.
>   */
> +#ifndef CONFIG_RCU_NOCB_CPU_ALL
>  int rcu_needs_cpu(int cpu, unsigned long *dj)
>  {
>  	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
> @@ -1726,6 +1729,7 @@ int rcu_needs_cpu(int cpu, unsigned long *dj)
>  	}
>  	return 0;
>  }
> +#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
>  
>  /*
>   * Prepare a CPU for idle from an RCU perspective.  The first major task
> -- 
> 1.8.1.5
>