Re: [PATCH tip/core/rcu 15/24] rcu: Directly drive RCU_USER_QS from Kconfig

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Thu, May 14, 2015 at 02:27:48AM +0200, Frederic Weisbecker wrote:
> 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@linux.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@kernel.org>
> > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > > Cc: Frederic Weisbecker <fweisbec@gmail.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@gmail.com>
> >     Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> Excellent! ACK+!

Very good!  I applied your Acked-by to both patches, please let me know
if you intended something else.

							Thanx, Paul

> 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
> > 
>