Eliminate redundant rcu_sysidle_state variable

RFC PATCH In review Paul E. McKenney 3 participants 5 messages Jul 23, 2014 – Jul 24, 2014 RCU

Share & tools

Paul E. McKenney

author

2014-07-23 16:29 UTC #0 lore raw

RFC PATCH 1/2 Eliminate redundant rcu_sysidle_state variable

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 <[email protected]>

kernel/rcu/tree_plugin.h +6 ~~-17~~

index 24f5bd54ca9b..e31fa71c4d3a 100644
@@ -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;

Paul E. McKenney

author

2014-07-23 16:30 UTC #1 lore raw

RFC PATCH 2/2 Don't track sysidle state if no nohz_full= CPUs

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 <[email protected]>

kernel/rcu/tree_plugin.h +18 -1

index e31fa71c4d3a..c31eb28ae8bb 100644
@@ -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)
 {

Frederic Weisbecker

Acked-by on v1 2/2

2014-07-24 14:58 UTC #2 lore raw

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

Quoted 8 lines · 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 <[email protected]>

Acked-by Frederic Weisbecker <[email protected]>

Pranith Kumar

Reviewed-by on v1 1/2

2014-07-23 23:43 UTC #3 lore raw

In reply to Paul E. McKenney

Quoted 7 lines · 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 <[email protected]>

Reviewed-by Pranith Kumar <[email protected]>

Quoted 74 lines

kernel/rcu/tree_plugin.h +6 ~~-17~~

index 24f5bd54ca9b..e31fa71c4d3a 100644
@@ -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;

Signature · 1 line

Pranith

Frederic Weisbecker

Acked-by on v1 1/2

2014-07-24 14:29 UTC #4 lore raw

In reply to Paul E. McKenney

Quoted 6 lines · 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 <[email protected]>

Acked-by Frederic Weisbecker <[email protected]>

Quoted 75 lines

kernel/rcu/tree_plugin.h +6 ~~-17~~

index 24f5bd54ca9b..e31fa71c4d3a 100644
@@ -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;