Date:	Mon, 24 Aug 2009 15:17:57 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josht@...ux.vnet.ibm.com, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org
Subject: Re: [PATCH -tip] v3 Renamings to increase RCU clarity.

Paul E. McKenney wrote:
> From: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> Make RCU-sched, RCU-bh, and RCU-preempt be underlying implementations,
> with "RCU" defined in terms of one of the three.  Update the outdated
> rcu_qsctr_inc() names, as these functions no longer increment anything.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  Documentation/RCU/trace.txt |    7 ++--
>  include/linux/rcupdate.h    |   21 ++++++++---
>  include/linux/rcupreempt.h  |    4 +-
>  include/linux/rcutree.h     |    8 +++--
>  kernel/rcupreempt.c         |    8 ++--
>  kernel/rcutree.c            |   80 +++++++++++++++++++++++++++----------------
>  kernel/rcutree.h            |    4 +-
>  kernel/rcutree_trace.c      |   20 +++++-----
>  kernel/sched.c              |    2 +-
>  kernel/softirq.c            |    4 +-
>  10 files changed, 95 insertions(+), 63 deletions(-)
> 
> diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
> index 02cced1..187bbf1 100644
> --- a/Documentation/RCU/trace.txt
> +++ b/Documentation/RCU/trace.txt
> @@ -191,8 +191,7 @@ rcu/rcuhier (which displays the struct rcu_node hierarchy).
>  
>  The output of "cat rcu/rcudata" looks as follows:
>  
> -rcu:
> -rcu:
> +rcu_sched:
>    0 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=10951/1 dn=0 df=1101 of=0 ri=36 ql=0 b=10
>    1 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=16117/1 dn=0 df=1015 of=0 ri=0 ql=0 b=10
>    2 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=1445/1 dn=0 df=1839 of=0 ri=0 ql=0 b=10
> @@ -306,7 +305,7 @@ comma-separated-variable spreadsheet format.
>  
>  The output of "cat rcu/rcugp" looks as follows:
>  
> -rcu: completed=33062  gpnum=33063
> +rcu_sched: completed=33062  gpnum=33063
>  rcu_bh: completed=464  gpnum=464
>  
>  Again, this output is for both "rcu" and "rcu_bh".  The fields are
> @@ -413,7 +412,7 @@ o	Each element of the form "1/1 0:127 ^0" represents one struct
>  
>  The output of "cat rcu/rcu_pending" looks as follows:
>  
> -rcu:
> +rcu_sched:
>    0 np=255892 qsp=53936 cbr=0 cng=14417 gpc=10033 gps=24320 nf=6445 nn=146741
>    1 np=261224 qsp=54638 cbr=0 cng=25723 gpc=16310 gps=2849 nf=5912 nn=155792
>    2 np=237496 qsp=49664 cbr=0 cng=2762 gpc=45478 gps=1762 nf=1201 nn=136629
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 3c89d6a..e920f0f 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -157,17 +157,28 @@ extern int rcu_scheduler_active;
>   * - call_rcu_sched() and rcu_barrier_sched()
>   * on the write-side to insure proper synchronization.
>   */
> -#define rcu_read_lock_sched() preempt_disable()
> -#define rcu_read_lock_sched_notrace() preempt_disable_notrace()
> +static inline void rcu_read_lock_sched(void)
> +{
> +	preempt_disable();
> +}
> +static inline void rcu_read_lock_sched_notrace(void)
> +{
> +	preempt_disable_notrace();
> +}

It need be marked "notrace". Sometimes a function marked "inline"
may not be inlined when it is compiled.

Lai.
>  
>  /*
>   * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
>   *
>   * See rcu_read_lock_sched for more information.
>   */
> -#define rcu_read_unlock_sched() preempt_enable()
> -#define rcu_read_unlock_sched_notrace() preempt_enable_notrace()
> -
> +static inline void rcu_read_unlock_sched(void)
> +{
> +	preempt_enable();
> +}
> +static inline void rcu_read_unlock_sched_notrace(void)
> +{
> +	preempt_enable_notrace();
> +}
>  
>  
>  /**
> diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h
> index f164ac9..2963f08 100644
> --- a/include/linux/rcupreempt.h
> +++ b/include/linux/rcupreempt.h
> @@ -40,8 +40,8 @@
>  #include <linux/cpumask.h>
>  #include <linux/seqlock.h>
>  
> -extern void rcu_qsctr_inc(int cpu);
> -static inline void rcu_bh_qsctr_inc(int cpu) { }
> +extern void rcu_sched_qs(int cpu);
> +static inline void rcu_bh_qs(int cpu) { }
>  
>  /*
>   * Someone might want to pass call_rcu_bh as a function pointer.
> diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
> index e37d5e2..a0852d0 100644
> --- a/include/linux/rcutree.h
> +++ b/include/linux/rcutree.h
> @@ -30,8 +30,8 @@
>  #ifndef __LINUX_RCUTREE_H
>  #define __LINUX_RCUTREE_H
>  
> -extern void rcu_qsctr_inc(int cpu);
> -extern void rcu_bh_qsctr_inc(int cpu);
> +extern void rcu_sched_qs(int cpu);
> +extern void rcu_bh_qs(int cpu);
>  
>  extern int rcu_pending(int cpu);
>  extern int rcu_needs_cpu(int cpu);
> @@ -73,7 +73,8 @@ static inline void __rcu_read_unlock_bh(void)
>  
>  #define __synchronize_sched() synchronize_rcu()
>  
> -#define call_rcu_sched(head, func) call_rcu(head, func)
> +extern void call_rcu_sched(struct rcu_head *head,
> +			   void (*func)(struct rcu_head *rcu));
>  
>  static inline void synchronize_rcu_expedited(void)
>  {
> @@ -91,6 +92,7 @@ extern void rcu_restart_cpu(int cpu);
>  
>  extern long rcu_batches_completed(void);
>  extern long rcu_batches_completed_bh(void);
> +extern long rcu_batches_completed_sched(void);
>  
>  static inline void rcu_init_sched(void)
>  {
> diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
> index 510898a..0eef9b7 100644
> --- a/kernel/rcupreempt.c
> +++ b/kernel/rcupreempt.c
> @@ -159,7 +159,7 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_dyntick_sched, rcu_dyntick_sched
>  	.dynticks = 1,
>  };
>  
> -void rcu_qsctr_inc(int cpu)
> +void rcu_sched_qs(int cpu)
>  {
>  	struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
>  
> @@ -967,12 +967,12 @@ void rcu_check_callbacks(int cpu, int user)
>  	 * If this CPU took its interrupt from user mode or from the
>  	 * idle loop, and this is not a nested interrupt, then
>  	 * this CPU has to have exited all prior preept-disable
> -	 * sections of code.  So increment the counter to note this.
> +	 * sections of code.  So invoke rcu_sched_qs() to note this.
>  	 *
>  	 * The memory barrier is needed to handle the case where
>  	 * writes from a preempt-disable section of code get reordered
>  	 * into schedule() by this CPU's write buffer.  So the memory
> -	 * barrier makes sure that the rcu_qsctr_inc() is seen by other
> +	 * barrier makes sure that the rcu_sched_qs() is seen by other
>  	 * CPUs to happen after any such write.
>  	 */
>  
> @@ -980,7 +980,7 @@ void rcu_check_callbacks(int cpu, int user)
>  	    (idle_cpu(cpu) && !in_softirq() &&
>  	     hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
>  		smp_mb();	/* Guard against aggressive schedule(). */
> -	     	rcu_qsctr_inc(cpu);
> +	     	rcu_sched_qs(cpu);
>  	}
>  
>  	rcu_check_mb(cpu);
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index a162f85..4d71d4e 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -74,26 +74,25 @@ EXPORT_SYMBOL_GPL(rcu_lock_map);
>  	.n_force_qs_ngp = 0, \
>  }
>  
> -struct rcu_state rcu_state = RCU_STATE_INITIALIZER(rcu_state);
> -DEFINE_PER_CPU(struct rcu_data, rcu_data);
> +struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched_state);
> +DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
>  
>  struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
>  DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
>  
>  /*
> - * Increment the quiescent state counter.
> - * The counter is a bit degenerated: We do not need to know
> + * Note a quiescent state.  Because we do not need to know
>   * how many quiescent states passed, just if there was at least
> - * one since the start of the grace period. Thus just a flag.
> + * one since the start of the grace period, this just sets a flag.
>   */
> -void rcu_qsctr_inc(int cpu)
> +void rcu_sched_qs(int cpu)
>  {
> -	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
> +	struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
>  	rdp->passed_quiesc = 1;
>  	rdp->passed_quiesc_completed = rdp->completed;
>  }
>  
> -void rcu_bh_qsctr_inc(int cpu)
> +void rcu_bh_qs(int cpu)
>  {
>  	struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
>  	rdp->passed_quiesc = 1;
> @@ -114,11 +113,21 @@ static int qlowmark = 100;	/* Once only this many pending, use blimit. */
>  static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
>  
>  /*
> + * Return the number of RCU-sched batches processed thus far for debug & stats.
> + */
> +long rcu_batches_completed_sched(void)
> +{
> +	return rcu_sched_state.completed;
> +}
> +EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
> +
> +/*
>   * Return the number of RCU batches processed thus far for debug & stats.
> + * @@@ placeholder, maps to rcu_batches_completed_sched().
>   */
>  long rcu_batches_completed(void)
>  {
> -	return rcu_state.completed;
> +	return rcu_batches_completed_sched();
>  }
>  EXPORT_SYMBOL_GPL(rcu_batches_completed);
>  
> @@ -310,7 +319,7 @@ void rcu_irq_exit(void)
>  	WARN_ON_RATELIMIT(rdtp->dynticks & 0x1, &rcu_rs);
>  
>  	/* If the interrupt queued a callback, get out of dyntick mode. */
> -	if (__get_cpu_var(rcu_data).nxtlist ||
> +	if (__get_cpu_var(rcu_sched_data).nxtlist ||
>  	    __get_cpu_var(rcu_bh_data).nxtlist)
>  		set_need_resched();
>  }
> @@ -847,7 +856,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
>  	/*
>  	 * Move callbacks from the outgoing CPU to the running CPU.
>  	 * Note that the outgoing CPU is now quiscent, so it is now
> -	 * (uncharacteristically) safe to access it rcu_data structure.
> +	 * (uncharacteristically) safe to access its rcu_data structure.
>  	 * Note also that we must carefully retain the order of the
>  	 * outgoing CPU's callbacks in order for rcu_barrier() to work
>  	 * correctly.  Finally, note that we start all the callbacks
> @@ -878,7 +887,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
>   */
>  static void rcu_offline_cpu(int cpu)
>  {
> -	__rcu_offline_cpu(cpu, &rcu_state);
> +	__rcu_offline_cpu(cpu, &rcu_sched_state);
>  	__rcu_offline_cpu(cpu, &rcu_bh_state);
>  }
>  
> @@ -973,17 +982,16 @@ void rcu_check_callbacks(int cpu, int user)
>  		 * Get here if this CPU took its interrupt from user
>  		 * mode or from the idle loop, and if this is not a
>  		 * nested interrupt.  In this case, the CPU is in
> -		 * a quiescent state, so count it.
> +		 * a quiescent state, so note it.
>  		 *
>  		 * No memory barrier is required here because both
> -		 * rcu_qsctr_inc() and rcu_bh_qsctr_inc() reference
> -		 * only CPU-local variables that other CPUs neither
> -		 * access nor modify, at least not while the corresponding
> -		 * CPU is online.
> +		 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
> +		 * variables that other CPUs neither access nor modify,
> +		 * at least not while the corresponding CPU is online.
>  		 */
>  
> -		rcu_qsctr_inc(cpu);
> -		rcu_bh_qsctr_inc(cpu);
> +		rcu_sched_qs(cpu);
> +		rcu_bh_qs(cpu);
>  
>  	} else if (!in_softirq()) {
>  
> @@ -991,10 +999,10 @@ void rcu_check_callbacks(int cpu, int user)
>  		 * Get here if this CPU did not take its interrupt from
>  		 * softirq, in other words, if it is not interrupting
>  		 * a rcu_bh read-side critical section.  This is an _bh
> -		 * critical section, so count it.
> +		 * critical section, so note it.
>  		 */
>  
> -		rcu_bh_qsctr_inc(cpu);
> +		rcu_bh_qs(cpu);
>  	}
>  	raise_softirq(RCU_SOFTIRQ);
>  }
> @@ -1174,7 +1182,8 @@ static void rcu_process_callbacks(struct softirq_action *unused)
>  	 */
>  	smp_mb(); /* See above block comment. */
>  
> -	__rcu_process_callbacks(&rcu_state, &__get_cpu_var(rcu_data));
> +	__rcu_process_callbacks(&rcu_sched_state,
> +				&__get_cpu_var(rcu_sched_data));
>  	__rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
>  
>  	/*
> @@ -1231,14 +1240,25 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
>  }
>  
>  /*
> - * Queue an RCU callback for invocation after a grace period.
> + * Queue an RCU-sched callback for invocation after a grace period.
> + */
> +void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
> +{
> +	__call_rcu(head, func, &rcu_sched_state);
> +}
> +EXPORT_SYMBOL_GPL(call_rcu_sched);
> +
> +/*
> + * @@@ Queue an RCU callback for invocation after a grace period.
> + * @@@ Placeholder pending rcutree_plugin.h.
>   */
>  void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
>  {
> -	__call_rcu(head, func, &rcu_state);
> +	call_rcu_sched(head, func);
>  }
>  EXPORT_SYMBOL_GPL(call_rcu);
>  
> +
>  /*
>   * Queue an RCU for invocation after a quicker grace period.
>   */
> @@ -1311,7 +1331,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
>   */
>  int rcu_pending(int cpu)
>  {
> -	return __rcu_pending(&rcu_state, &per_cpu(rcu_data, cpu)) ||
> +	return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
>  	       __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu));
>  }
>  
> @@ -1324,7 +1344,7 @@ int rcu_pending(int cpu)
>  int rcu_needs_cpu(int cpu)
>  {
>  	/* RCU callbacks either ready or pending? */
> -	return per_cpu(rcu_data, cpu).nxtlist ||
> +	return per_cpu(rcu_sched_data, cpu).nxtlist ||
>  	       per_cpu(rcu_bh_data, cpu).nxtlist;
>  }
>  
> @@ -1418,7 +1438,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
>  
>  static void __cpuinit rcu_online_cpu(int cpu)
>  {
> -	rcu_init_percpu_data(cpu, &rcu_state);
> +	rcu_init_percpu_data(cpu, &rcu_sched_state);
>  	rcu_init_percpu_data(cpu, &rcu_bh_state);
>  }
>  
> @@ -1545,10 +1565,10 @@ void __init __rcu_init(void)
>  #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
>  	printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n");
>  #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
> -	rcu_init_one(&rcu_state);
> -	RCU_DATA_PTR_INIT(&rcu_state, rcu_data);
> +	rcu_init_one(&rcu_sched_state);
> +	RCU_DATA_PTR_INIT(&rcu_sched_state, rcu_sched_data);
>  	for_each_possible_cpu(i)
> -		rcu_boot_init_percpu_data(i, &rcu_state);
> +		rcu_boot_init_percpu_data(i, &rcu_sched_state);
>  	rcu_init_one(&rcu_bh_state);
>  	RCU_DATA_PTR_INIT(&rcu_bh_state, rcu_bh_data);
>  	for_each_possible_cpu(i)
> diff --git a/kernel/rcutree.h b/kernel/rcutree.h
> index 7cc830a..0024e5d 100644
> --- a/kernel/rcutree.h
> +++ b/kernel/rcutree.h
> @@ -238,8 +238,8 @@ struct rcu_state {
>  /*
>   * RCU implementation internal declarations:
>   */
> -extern struct rcu_state rcu_state;
> -DECLARE_PER_CPU(struct rcu_data, rcu_data);
> +extern struct rcu_state rcu_sched_state;
> +DECLARE_PER_CPU(struct rcu_data, rcu_sched_data);
>  
>  extern struct rcu_state rcu_bh_state;
>  DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
> diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
> index 0cb52b8..236c050 100644
> --- a/kernel/rcutree_trace.c
> +++ b/kernel/rcutree_trace.c
> @@ -77,8 +77,8 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
>  
>  static int show_rcudata(struct seq_file *m, void *unused)
>  {
> -	seq_puts(m, "rcu:\n");
> -	PRINT_RCU_DATA(rcu_data, print_one_rcu_data, m);
> +	seq_puts(m, "rcu_sched:\n");
> +	PRINT_RCU_DATA(rcu_sched_data, print_one_rcu_data, m);
>  	seq_puts(m, "rcu_bh:\n");
>  	PRINT_RCU_DATA(rcu_bh_data, print_one_rcu_data, m);
>  	return 0;
> @@ -125,8 +125,8 @@ static int show_rcudata_csv(struct seq_file *m, void *unused)
>  	seq_puts(m, "\"dt\",\"dt nesting\",\"dn\",\"df\",");
>  #endif /* #ifdef CONFIG_NO_HZ */
>  	seq_puts(m, "\"of\",\"ri\",\"ql\",\"b\"\n");
> -	seq_puts(m, "\"rcu:\"\n");
> -	PRINT_RCU_DATA(rcu_data, print_one_rcu_data_csv, m);
> +	seq_puts(m, "\"rcu_sched:\"\n");
> +	PRINT_RCU_DATA(rcu_sched_data, print_one_rcu_data_csv, m);
>  	seq_puts(m, "\"rcu_bh:\"\n");
>  	PRINT_RCU_DATA(rcu_bh_data, print_one_rcu_data_csv, m);
>  	return 0;
> @@ -172,8 +172,8 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
>  
>  static int show_rcuhier(struct seq_file *m, void *unused)
>  {
> -	seq_puts(m, "rcu:\n");
> -	print_one_rcu_state(m, &rcu_state);
> +	seq_puts(m, "rcu_sched:\n");
> +	print_one_rcu_state(m, &rcu_sched_state);
>  	seq_puts(m, "rcu_bh:\n");
>  	print_one_rcu_state(m, &rcu_bh_state);
>  	return 0;
> @@ -194,8 +194,8 @@ static struct file_operations rcuhier_fops = {
>  
>  static int show_rcugp(struct seq_file *m, void *unused)
>  {
> -	seq_printf(m, "rcu: completed=%ld  gpnum=%ld\n",
> -		   rcu_state.completed, rcu_state.gpnum);
> +	seq_printf(m, "rcu_sched: completed=%ld  gpnum=%ld\n",
> +		   rcu_sched_state.completed, rcu_sched_state.gpnum);
>  	seq_printf(m, "rcu_bh: completed=%ld  gpnum=%ld\n",
>  		   rcu_bh_state.completed, rcu_bh_state.gpnum);
>  	return 0;
> @@ -244,8 +244,8 @@ static void print_rcu_pendings(struct seq_file *m, struct rcu_state *rsp)
>  
>  static int show_rcu_pending(struct seq_file *m, void *unused)
>  {
> -	seq_puts(m, "rcu:\n");
> -	print_rcu_pendings(m, &rcu_state);
> +	seq_puts(m, "rcu_sched:\n");
> +	print_rcu_pendings(m, &rcu_sched_state);
>  	seq_puts(m, "rcu_bh:\n");
>  	print_rcu_pendings(m, &rcu_bh_state);
>  	return 0;
> diff --git a/kernel/sched.c b/kernel/sched.c
> index cda8b81..c9beca6 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -5325,7 +5325,7 @@ need_resched:
>  	preempt_disable();
>  	cpu = smp_processor_id();
>  	rq = cpu_rq(cpu);
> -	rcu_qsctr_inc(cpu);
> +	rcu_sched_qs(cpu);
>  	prev = rq->curr;
>  	switch_count = &prev->nivcsw;
>  
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index eb5e131..7db2506 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -227,7 +227,7 @@ restart:
>  				preempt_count() = prev_count;
>  			}
>  
> -			rcu_bh_qsctr_inc(cpu);
> +			rcu_bh_qs(cpu);
>  		}
>  		h++;
>  		pending >>= 1;
> @@ -721,7 +721,7 @@ static int ksoftirqd(void * __bind_cpu)
>  			preempt_enable_no_resched();
>  			cond_resched();
>  			preempt_disable();
> -			rcu_qsctr_inc((long)__bind_cpu);
> +			rcu_sched_qs((long)__bind_cpu);
>  		}
>  		preempt_enable();
>  		set_current_state(TASK_INTERRUPTIBLE);


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