[PATCH RFC tip/core/rcu 1/2] Eliminate redundant rcu_sysidle_state variable

[PATCH RFC tip/core/rcu 1/2] Eliminate redundant rcu_sysidle_state variable

[Paul E. McKenney]

Now that we have rcu_state_p, which references rcu_preempt_state for
TREE_PREEMPT_RCU and rcu_sched_state for TREE_RCU, we don't need a
separate rcu_sysidle_state variable.  This commit therefore eliminates
rcu_preempt_state in favor of rcu_state_p.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 24f5bd54ca9b..e31fa71c4d3a 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2662,16 +2662,6 @@ static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
 
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
 
-/*
- * Define RCU flavor that holds sysidle state.  This needs to be the
- * most active flavor of RCU.
- */
-#ifdef CONFIG_PREEMPT_RCU
-static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
-#else /* #ifdef CONFIG_PREEMPT_RCU */
-static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
-#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
-
 static int full_sysidle_state;		/* Current system-idle state. */
 #define RCU_SYSIDLE_NOT		0	/* Some CPU is not idle. */
 #define RCU_SYSIDLE_SHORT	1	/* All CPUs idle for brief period. */
@@ -2813,7 +2803,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
 	 * not the flavor of RCU that tracks sysidle state, or if this
 	 * is an offline or the timekeeping CPU, nothing to do.
 	 */
-	if (!*isidle || rdp->rsp != rcu_sysidle_state ||
+	if (!*isidle || rdp->rsp != rcu_state_p ||
 	    cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
 		return;
 	if (rcu_gp_in_progress(rdp->rsp))
@@ -2839,7 +2829,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
  */
 static bool is_sysidle_rcu_state(struct rcu_state *rsp)
 {
-	return rsp == rcu_sysidle_state;
+	return rsp == rcu_state_p;
 }
 
 /*
@@ -2917,7 +2907,7 @@ static void rcu_sysidle_cancel(void)
 static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
 			       unsigned long maxj, bool gpkt)
 {
-	if (rsp != rcu_sysidle_state)
+	if (rsp != rcu_state_p)
 		return;  /* Wrong flavor, ignore. */
 	if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
 		return;  /* Running state machine from timekeeping CPU. */
@@ -2986,13 +2976,12 @@ bool rcu_sys_is_idle(void)
 
 			/* Scan all the CPUs looking for nonidle CPUs. */
 			for_each_possible_cpu(cpu) {
-				rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
+				rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
 				rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
 				if (!isidle)
 					break;
 			}
-			rcu_sysidle_report(rcu_sysidle_state,
-					   isidle, maxj, false);
+			rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
 			oldrss = rss;
 			rss = ACCESS_ONCE(full_sysidle_state);
 		}
@@ -3019,7 +3008,7 @@ bool rcu_sys_is_idle(void)
 	 * provided by the memory allocator.
 	 */
 	if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
-	    !rcu_gp_in_progress(rcu_sysidle_state) &&
+	    !rcu_gp_in_progress(rcu_state_p) &&
 	    !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
 		call_rcu(&rsh.rh, rcu_sysidle_cb);
 	return false;

[PATCH RFC tip/core/rcu 2/2] Don't track sysidle state if no nohz_full= CPUs

[Paul E. McKenney]

If there are no nohz_full= CPUs, then there is currently no reason to
track sysidle state.  This commit therefore short-circuits this state
tracking if !tick_nohz_full_enabled().

Note that these checks will need to be revisited if nohz_full= state
can ever be changed at runtime.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index e31fa71c4d3a..c31eb28ae8bb 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2679,6 +2679,10 @@ static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
 {
 	unsigned long j;
 
+	/* If there are no nohz_full= CPUs, no need to track this. */
+	if (!tick_nohz_full_enabled())
+		return;
+
 	/* Adjust nesting, check for fully idle. */
 	if (irq) {
 		rdtp->dynticks_idle_nesting--;
@@ -2744,6 +2748,10 @@ void rcu_sysidle_force_exit(void)
  */
 static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
 {
+	/* If there are no nohz_full= CPUs, no need to track this. */
+	if (!tick_nohz_full_enabled())
+		return;
+
 	/* Adjust nesting, check for already non-idle. */
 	if (irq) {
 		rdtp->dynticks_idle_nesting++;
@@ -2798,6 +2806,10 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
 	unsigned long j;
 	struct rcu_dynticks *rdtp = rdp->dynticks;
 
+	/* If there are no nohz_full= CPUs, don't check system-wide idleness. */
+	if (!tick_nohz_full_enabled())
+		return;
+
 	/*
 	 * If some other CPU has already reported non-idle, if this is
 	 * not the flavor of RCU that tracks sysidle state, or if this
@@ -2924,6 +2936,10 @@ static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
 				  unsigned long maxj)
 {
+	/* If there are no nohz_full= CPUs, no need to track this. */
+	if (!tick_nohz_full_enabled())
+		return;
+
 	rcu_sysidle_report(rsp, isidle, maxj, true);
 }
 
@@ -2950,7 +2966,8 @@ static void rcu_sysidle_cb(struct rcu_head *rhp)
 
 /*
  * Check to see if the system is fully idle, other than the timekeeping CPU.
- * The caller must have disabled interrupts.
+ * The caller must have disabled interrupts.  This is not intended to be
+ * called unless tick_nohz_full_enabled().
  */
 bool rcu_sys_is_idle(void)
 {

Re: [PATCH RFC tip/core/rcu 1/2] Eliminate redundant rcu_sysidle_state variable

[Pranith Kumar]

On Wed, Jul 23, 2014 at 12:28 PM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
> Now that we have rcu_state_p, which references rcu_preempt_state for
> TREE_PREEMPT_RCU and rcu_sched_state for TREE_RCU, we don't need a
> separate rcu_sysidle_state variable.  This commit therefore eliminates
> rcu_preempt_state in favor of rcu_state_p.
>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>

Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>


> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 24f5bd54ca9b..e31fa71c4d3a 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2662,16 +2662,6 @@ static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
>
>  #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
>
> -/*
> - * Define RCU flavor that holds sysidle state.  This needs to be the
> - * most active flavor of RCU.
> - */
> -#ifdef CONFIG_PREEMPT_RCU
> -static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
> -#else /* #ifdef CONFIG_PREEMPT_RCU */
> -static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
> -#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
> -
>  static int full_sysidle_state;         /* Current system-idle state. */
>  #define RCU_SYSIDLE_NOT                0       /* Some CPU is not idle. */
>  #define RCU_SYSIDLE_SHORT      1       /* All CPUs idle for brief period. */
> @@ -2813,7 +2803,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
>          * not the flavor of RCU that tracks sysidle state, or if this
>          * is an offline or the timekeeping CPU, nothing to do.
>          */
> -       if (!*isidle || rdp->rsp != rcu_sysidle_state ||
> +       if (!*isidle || rdp->rsp != rcu_state_p ||
>             cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
>                 return;
>         if (rcu_gp_in_progress(rdp->rsp))
> @@ -2839,7 +2829,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
>   */
>  static bool is_sysidle_rcu_state(struct rcu_state *rsp)
>  {
> -       return rsp == rcu_sysidle_state;
> +       return rsp == rcu_state_p;
>  }
>
>  /*
> @@ -2917,7 +2907,7 @@ static void rcu_sysidle_cancel(void)
>  static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
>                                unsigned long maxj, bool gpkt)
>  {
> -       if (rsp != rcu_sysidle_state)
> +       if (rsp != rcu_state_p)
>                 return;  /* Wrong flavor, ignore. */
>         if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
>                 return;  /* Running state machine from timekeeping CPU. */
> @@ -2986,13 +2976,12 @@ bool rcu_sys_is_idle(void)
>
>                         /* Scan all the CPUs looking for nonidle CPUs. */
>                         for_each_possible_cpu(cpu) {
> -                               rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
> +                               rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
>                                 rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
>                                 if (!isidle)
>                                         break;
>                         }
> -                       rcu_sysidle_report(rcu_sysidle_state,
> -                                          isidle, maxj, false);
> +                       rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
>                         oldrss = rss;
>                         rss = ACCESS_ONCE(full_sysidle_state);
>                 }
> @@ -3019,7 +3008,7 @@ bool rcu_sys_is_idle(void)
>          * provided by the memory allocator.
>          */
>         if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
> -           !rcu_gp_in_progress(rcu_sysidle_state) &&
> +           !rcu_gp_in_progress(rcu_state_p) &&
>             !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
>                 call_rcu(&rsh.rh, rcu_sysidle_cb);
>         return false;
>



-- 
Pranith

Re: [PATCH RFC tip/core/rcu 1/2] Eliminate redundant rcu_sysidle_state variable

[Frederic Weisbecker]

On Wed, Jul 23, 2014 at 09:28:52AM -0700, Paul E. McKenney wrote:
> Now that we have rcu_state_p, which references rcu_preempt_state for
> TREE_PREEMPT_RCU and rcu_sched_state for TREE_RCU, we don't need a
> separate rcu_sysidle_state variable.  This commit therefore eliminates
> rcu_preempt_state in favor of rcu_state_p.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>

> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 24f5bd54ca9b..e31fa71c4d3a 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2662,16 +2662,6 @@ static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
>  
>  #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
>  
> -/*
> - * Define RCU flavor that holds sysidle state.  This needs to be the
> - * most active flavor of RCU.
> - */
> -#ifdef CONFIG_PREEMPT_RCU
> -static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
> -#else /* #ifdef CONFIG_PREEMPT_RCU */
> -static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
> -#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
> -
>  static int full_sysidle_state;		/* Current system-idle state. */
>  #define RCU_SYSIDLE_NOT		0	/* Some CPU is not idle. */
>  #define RCU_SYSIDLE_SHORT	1	/* All CPUs idle for brief period. */
> @@ -2813,7 +2803,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
>  	 * not the flavor of RCU that tracks sysidle state, or if this
>  	 * is an offline or the timekeeping CPU, nothing to do.
>  	 */
> -	if (!*isidle || rdp->rsp != rcu_sysidle_state ||
> +	if (!*isidle || rdp->rsp != rcu_state_p ||
>  	    cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
>  		return;
>  	if (rcu_gp_in_progress(rdp->rsp))
> @@ -2839,7 +2829,7 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
>   */
>  static bool is_sysidle_rcu_state(struct rcu_state *rsp)
>  {
> -	return rsp == rcu_sysidle_state;
> +	return rsp == rcu_state_p;
>  }
>  
>  /*
> @@ -2917,7 +2907,7 @@ static void rcu_sysidle_cancel(void)
>  static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
>  			       unsigned long maxj, bool gpkt)
>  {
> -	if (rsp != rcu_sysidle_state)
> +	if (rsp != rcu_state_p)
>  		return;  /* Wrong flavor, ignore. */
>  	if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
>  		return;  /* Running state machine from timekeeping CPU. */
> @@ -2986,13 +2976,12 @@ bool rcu_sys_is_idle(void)
>  
>  			/* Scan all the CPUs looking for nonidle CPUs. */
>  			for_each_possible_cpu(cpu) {
> -				rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
> +				rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
>  				rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
>  				if (!isidle)
>  					break;
>  			}
> -			rcu_sysidle_report(rcu_sysidle_state,
> -					   isidle, maxj, false);
> +			rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
>  			oldrss = rss;
>  			rss = ACCESS_ONCE(full_sysidle_state);
>  		}
> @@ -3019,7 +3008,7 @@ bool rcu_sys_is_idle(void)
>  	 * provided by the memory allocator.
>  	 */
>  	if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
> -	    !rcu_gp_in_progress(rcu_sysidle_state) &&
> +	    !rcu_gp_in_progress(rcu_state_p) &&
>  	    !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
>  		call_rcu(&rsh.rh, rcu_sysidle_cb);
>  	return false;
> 

Re: [PATCH RFC tip/core/rcu 2/2] Don't track sysidle state if no nohz_full= CPUs

[Frederic Weisbecker]

On Wed, Jul 23, 2014 at 09:29:51AM -0700, Paul E. McKenney wrote:
> If there are no nohz_full= CPUs, then there is currently no reason to
> track sysidle state.  This commit therefore short-circuits this state
> tracking if !tick_nohz_full_enabled().
> 
> Note that these checks will need to be revisited if nohz_full= state
> can ever be changed at runtime.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>