linux-kernel - Re: [PATCH tip/core/rcu 15/24] rcu: Directly drive RCU_USER

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Date:	Thu, 14 May 2015 02:27:48 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
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,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 15/24] rcu: Directly drive RCU_USER_QS from
 Kconfig

On Wed, May 13, 2015 at 10:45:05AM -0700, Paul E. McKenney wrote:
> On Wed, May 13, 2015 at 02:37:52AM +0200, Frederic Weisbecker wrote:
> > On Tue, May 12, 2015 at 03:30:45PM -0700, Paul E. McKenney wrote:
> > > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > > 
> > > Currently, Kconfig will ask the user whether RCU_USER_QS should be set.
> > > This is silly because Kconfig already has all the information that it
> > > needs to set this parameter.  This commit therefore directly drives
> > > the value of RCU_USER_QS via NO_HZ_FULL's "select" statement.
> > > 
> > > Reported-by: Ingo Molnar <mingo@...nel.org>
> > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > > Cc: Frederic Weisbecker <fweisbec@...il.com>
> > 
> > ACK. And we should remove it completely and use NO_HZ_FULL instead.
> > There won't seem to be more users.
> 
> Good point!  I have queued the patch shown below for 4.3.
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
>     rcu: Drop RCU_USER_QS in favor of NO_HZ_FULL
>     
>     The RCU_USER_QS Kconfig parameter is now just a synonym for NO_HZ_FULL,
>     so this commit eliminates RCU_USER_QS, replacing all uses with NO_HZ_FULL.
>     
>     Reported-by: Frederic Weisbecker <fweisbec@...il.com>
>     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

Excellent! ACK+!

Thanks.

> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 03a899aabd17..18e377b92875 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -307,7 +307,7 @@ static inline void rcu_sysrq_end(void)
>  }
>  #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
>  
> -#ifdef CONFIG_RCU_USER_QS
> +#ifdef CONFIG_NO_HZ_FULL
>  void rcu_user_enter(void);
>  void rcu_user_exit(void);
>  #else
> @@ -315,7 +315,7 @@ static inline void rcu_user_enter(void) { }
>  static inline void rcu_user_exit(void) { }
>  static inline void rcu_user_hooks_switch(struct task_struct *prev,
>  					 struct task_struct *next) { }
> -#endif /* CONFIG_RCU_USER_QS */
> +#endif /* CONFIG_NO_HZ_FULL */
>  
>  #ifdef CONFIG_RCU_NOCB_CPU
>  void rcu_init_nohz(void);
> diff --git a/init/Kconfig b/init/Kconfig
> index 4c08197044f1..5b8726c10685 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -537,15 +537,6 @@ config RCU_STALL_COMMON
>  config CONTEXT_TRACKING
>         bool
>  
> -config RCU_USER_QS
> -	bool
> -	help
> -	  This option sets hooks on kernel / userspace boundaries and
> -	  puts RCU in extended quiescent state when the CPU runs in
> -	  userspace. It means that when a CPU runs in userspace, it is
> -	  excluded from the global RCU state machine and thus doesn't
> -	  try to keep the timer tick on for RCU.
> -
>  config CONTEXT_TRACKING_FORCE
>  	bool "Force context tracking"
>  	depends on CONTEXT_TRACKING
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 7651d7dd982c..012cbee9d354 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -696,7 +696,7 @@ void rcu_idle_enter(void)
>  }
>  EXPORT_SYMBOL_GPL(rcu_idle_enter);
>  
> -#ifdef CONFIG_RCU_USER_QS
> +#ifdef CONFIG_NO_HZ_FULL
>  /**
>   * rcu_user_enter - inform RCU that we are resuming userspace.
>   *
> @@ -709,7 +709,7 @@ void rcu_user_enter(void)
>  {
>  	rcu_eqs_enter(1);
>  }
> -#endif /* CONFIG_RCU_USER_QS */
> +#endif /* CONFIG_NO_HZ_FULL */
>  
>  /**
>   * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
> @@ -823,7 +823,7 @@ void rcu_idle_exit(void)
>  }
>  EXPORT_SYMBOL_GPL(rcu_idle_exit);
>  
> -#ifdef CONFIG_RCU_USER_QS
> +#ifdef CONFIG_NO_HZ_FULL
>  /**
>   * rcu_user_exit - inform RCU that we are exiting userspace.
>   *
> @@ -834,7 +834,7 @@ void rcu_user_exit(void)
>  {
>  	rcu_eqs_exit(1);
>  }
> -#endif /* CONFIG_RCU_USER_QS */
> +#endif /* CONFIG_NO_HZ_FULL */
>  
>  /**
>   * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
> diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
> index 579ce1b929af..4008d9f95dd7 100644
> --- a/kernel/time/Kconfig
> +++ b/kernel/time/Kconfig
> @@ -92,12 +92,10 @@ config NO_HZ_FULL
>  	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
>  	# We need at least one periodic CPU for timekeeping
>  	depends on SMP
> -	# RCU_USER_QS dependency
>  	depends on HAVE_CONTEXT_TRACKING
>  	# VIRT_CPU_ACCOUNTING_GEN dependency
>  	depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
>  	select NO_HZ_COMMON
> -	select RCU_USER_QS
>  	select RCU_NOCB_CPU
>  	select VIRT_CPU_ACCOUNTING_GEN
>  	select IRQ_WORK
> 
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