rcu: Remove nohz_full full-system-idle state machine

The NO_HZ_FULL_SYSIDLE full-system-idle capability was added in 2013
by commit 0edd1b1784cb ("nohz_full: Add full-system-idle state machine"),
but has not been used.  This commit therefore removes it.

If it turns out to be needed later, this commit can always be reverted.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 429 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0553d9f..f524d96 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2563,429 +2563,6 @@ static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
 #endif /* #ifdef CONFIG_NO_HZ_FULL */
 }
 
-
-#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
-
-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. */
-#define RCU_SYSIDLE_LONG	2	/* All CPUs idle for long enough. */
-#define RCU_SYSIDLE_FULL	3	/* All CPUs idle, ready for sysidle. */
-#define RCU_SYSIDLE_FULL_NOTED	4	/* Actually entered sysidle state. */
-
-/*
- * Invoked to note exit from irq or task transition to idle.  Note that
- * usermode execution does -not- count as idle here!  After all, we want
- * to detect full-system idle states, not RCU quiescent states and grace
- * periods.  The caller must have disabled interrupts.
- */
-static void rcu_sysidle_enter(int irq)
-{
-	unsigned long j;
-	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-
-	RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_sysidle_enter() invoked with irqs enabled!!!");
-
-	/* 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--;
-		WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
-		if (rdtp->dynticks_idle_nesting != 0)
-			return;  /* Still not fully idle. */
-	} else {
-		if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
-		    DYNTICK_TASK_NEST_VALUE) {
-			rdtp->dynticks_idle_nesting = 0;
-		} else {
-			rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
-			WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
-			return;  /* Still not fully idle. */
-		}
-	}
-
-	/* Record start of fully idle period. */
-	j = jiffies;
-	WRITE_ONCE(rdtp->dynticks_idle_jiffies, j);
-	smp_mb__before_atomic();
-	atomic_inc(&rdtp->dynticks_idle);
-	smp_mb__after_atomic();
-	WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
-}
-
-/*
- * Unconditionally force exit from full system-idle state.  This is
- * invoked when a normal CPU exits idle, but must be called separately
- * for the timekeeping CPU (tick_do_timer_cpu).  The reason for this
- * is that the timekeeping CPU is permitted to take scheduling-clock
- * interrupts while the system is in system-idle state, and of course
- * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
- * interrupt from any other type of interrupt.
- */
-void rcu_sysidle_force_exit(void)
-{
-	int oldstate = READ_ONCE(full_sysidle_state);
-	int newoldstate;
-
-	/*
-	 * Each pass through the following loop attempts to exit full
-	 * system-idle state.  If contention proves to be a problem,
-	 * a trylock-based contention tree could be used here.
-	 */
-	while (oldstate > RCU_SYSIDLE_SHORT) {
-		newoldstate = cmpxchg(&full_sysidle_state,
-				      oldstate, RCU_SYSIDLE_NOT);
-		if (oldstate == newoldstate &&
-		    oldstate == RCU_SYSIDLE_FULL_NOTED) {
-			rcu_kick_nohz_cpu(tick_do_timer_cpu);
-			return; /* We cleared it, done! */
-		}
-		oldstate = newoldstate;
-	}
-	smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
-}
-
-/*
- * Invoked to note entry to irq or task transition from idle.  Note that
- * usermode execution does -not- count as idle here!  The caller must
- * have disabled interrupts.
- */
-static void rcu_sysidle_exit(int irq)
-{
-	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-
-	RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_sysidle_exit() invoked with irqs enabled!!!");
-
-	/* 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++;
-		WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
-		if (rdtp->dynticks_idle_nesting != 1)
-			return; /* Already non-idle. */
-	} else {
-		/*
-		 * Allow for irq misnesting.  Yes, it really is possible
-		 * to enter an irq handler then never leave it, and maybe
-		 * also vice versa.  Handle both possibilities.
-		 */
-		if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
-			rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
-			WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
-			return; /* Already non-idle. */
-		} else {
-			rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
-		}
-	}
-
-	/* Record end of idle period. */
-	smp_mb__before_atomic();
-	atomic_inc(&rdtp->dynticks_idle);
-	smp_mb__after_atomic();
-	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
-
-	/*
-	 * If we are the timekeeping CPU, we are permitted to be non-idle
-	 * during a system-idle state.  This must be the case, because
-	 * the timekeeping CPU has to take scheduling-clock interrupts
-	 * during the time that the system is transitioning to full
-	 * system-idle state.  This means that the timekeeping CPU must
-	 * invoke rcu_sysidle_force_exit() directly if it does anything
-	 * more than take a scheduling-clock interrupt.
-	 */
-	if (smp_processor_id() == tick_do_timer_cpu)
-		return;
-
-	/* Update system-idle state: We are clearly no longer fully idle! */
-	rcu_sysidle_force_exit();
-}
-
-/*
- * Check to see if the current CPU is idle.  Note that usermode execution
- * does not count as idle.  The caller must have disabled interrupts,
- * and must be running on tick_do_timer_cpu.
- */
-static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
-				  unsigned long *maxj)
-{
-	int cur;
-	unsigned long j;
-	struct rcu_dynticks *rdtp = rdp->dynticks;
-
-	RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_sysidle_check_cpu() invoked with irqs enabled!!!");
-
-	/* 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
-	 * is an offline or the timekeeping CPU, nothing to do.
-	 */
-	if (!*isidle || rdp->rsp != rcu_state_p ||
-	    cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
-		return;
-	/* Verify affinity of current kthread. */
-	WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
-
-	/* Pick up current idle and NMI-nesting counter and check. */
-	cur = atomic_read(&rdtp->dynticks_idle);
-	if (cur & 0x1) {
-		*isidle = false; /* We are not idle! */
-		return;
-	}
-	smp_mb(); /* Read counters before timestamps. */
-
-	/* Pick up timestamps. */
-	j = READ_ONCE(rdtp->dynticks_idle_jiffies);
-	/* If this CPU entered idle more recently, update maxj timestamp. */
-	if (ULONG_CMP_LT(*maxj, j))
-		*maxj = j;
-}
-
-/*
- * Is this the flavor of RCU that is handling full-system idle?
- */
-static bool is_sysidle_rcu_state(struct rcu_state *rsp)
-{
-	return rsp == rcu_state_p;
-}
-
-/*
- * Return a delay in jiffies based on the number of CPUs, rcu_node
- * leaf fanout, and jiffies tick rate.  The idea is to allow larger
- * systems more time to transition to full-idle state in order to
- * avoid the cache thrashing that otherwise occur on the state variable.
- * Really small systems (less than a couple of tens of CPUs) should
- * instead use a single global atomically incremented counter, and later
- * versions of this will automatically reconfigure themselves accordingly.
- */
-static unsigned long rcu_sysidle_delay(void)
-{
-	if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
-		return 0;
-	return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
-}
-
-/*
- * Advance the full-system-idle state.  This is invoked when all of
- * the non-timekeeping CPUs are idle.
- */
-static void rcu_sysidle(unsigned long j)
-{
-	/* Check the current state. */
-	switch (READ_ONCE(full_sysidle_state)) {
-	case RCU_SYSIDLE_NOT:
-
-		/* First time all are idle, so note a short idle period. */
-		WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_SHORT);
-		break;
-
-	case RCU_SYSIDLE_SHORT:
-
-		/*
-		 * Idle for a bit, time to advance to next state?
-		 * cmpxchg failure means race with non-idle, let them win.
-		 */
-		if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
-			(void)cmpxchg(&full_sysidle_state,
-				      RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
-		break;
-
-	case RCU_SYSIDLE_LONG:
-
-		/*
-		 * Do an additional check pass before advancing to full.
-		 * cmpxchg failure means race with non-idle, let them win.
-		 */
-		if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
-			(void)cmpxchg(&full_sysidle_state,
-				      RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
-		break;
-
-	default:
-		break;
-	}
-}
-
-/*
- * Found a non-idle non-timekeeping CPU, so kick the system-idle state
- * back to the beginning.
- */
-static void rcu_sysidle_cancel(void)
-{
-	smp_mb();
-	if (full_sysidle_state > RCU_SYSIDLE_SHORT)
-		WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_NOT);
-}
-
-/*
- * Update the sysidle state based on the results of a force-quiescent-state
- * scan of the CPUs' dyntick-idle state.
- */
-static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
-			       unsigned long maxj, bool gpkt)
-{
-	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. */
-	if (isidle)
-		rcu_sysidle(maxj);    /* More idle! */
-	else
-		rcu_sysidle_cancel(); /* Idle is over. */
-}
-
-/*
- * Wrapper for rcu_sysidle_report() when called from the grace-period
- * kthread's context.
- */
-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);
-}
-
-/* Callback and function for forcing an RCU grace period. */
-struct rcu_sysidle_head {
-	struct rcu_head rh;
-	int inuse;
-};
-
-static void rcu_sysidle_cb(struct rcu_head *rhp)
-{
-	struct rcu_sysidle_head *rshp;
-
-	/*
-	 * The following memory barrier is needed to replace the
-	 * memory barriers that would normally be in the memory
-	 * allocator.
-	 */
-	smp_mb();  /* grace period precedes setting inuse. */
-
-	rshp = container_of(rhp, struct rcu_sysidle_head, rh);
-	WRITE_ONCE(rshp->inuse, 0);
-}
-
-/*
- * Check to see if the system is fully idle, other than the timekeeping CPU.
- * The caller must have disabled interrupts.  This is not intended to be
- * called unless tick_nohz_full_enabled().
- */
-bool rcu_sys_is_idle(void)
-{
-	static struct rcu_sysidle_head rsh;
-	int rss = READ_ONCE(full_sysidle_state);
-
-	RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_sys_is_idle() invoked with irqs enabled!!!");
-
-	if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
-		return false;
-
-	/* Handle small-system case by doing a full scan of CPUs. */
-	if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
-		int oldrss = rss - 1;
-
-		/*
-		 * One pass to advance to each state up to _FULL.
-		 * Give up if any pass fails to advance the state.
-		 */
-		while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
-			int cpu;
-			bool isidle = true;
-			unsigned long maxj = jiffies - ULONG_MAX / 4;
-			struct rcu_data *rdp;
-
-			/* Scan all the CPUs looking for nonidle CPUs. */
-			for_each_possible_cpu(cpu) {
-				rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
-				rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
-				if (!isidle)
-					break;
-			}
-			rcu_sysidle_report(rcu_state_p, isidle, maxj, false);
-			oldrss = rss;
-			rss = READ_ONCE(full_sysidle_state);
-		}
-	}
-
-	/* If this is the first observation of an idle period, record it. */
-	if (rss == RCU_SYSIDLE_FULL) {
-		rss = cmpxchg(&full_sysidle_state,
-			      RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
-		return rss == RCU_SYSIDLE_FULL;
-	}
-
-	smp_mb(); /* ensure rss load happens before later caller actions. */
-
-	/* If already fully idle, tell the caller (in case of races). */
-	if (rss == RCU_SYSIDLE_FULL_NOTED)
-		return true;
-
-	/*
-	 * If we aren't there yet, and a grace period is not in flight,
-	 * initiate a grace period.  Either way, tell the caller that
-	 * we are not there yet.  We use an xchg() rather than an assignment
-	 * to make up for the memory barriers that would otherwise be
-	 * provided by the memory allocator.
-	 */
-	if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
-	    !rcu_gp_in_progress(rcu_state_p) &&
-	    !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
-		call_rcu(&rsh.rh, rcu_sysidle_cb);
-	return false;
-}
-
-/*
- * Initialize dynticks sysidle state for CPUs coming online.
- */
-static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
-{
-	rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
-}
-
-#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
-
-static void rcu_sysidle_enter(int irq)
-{
-}
-
-static void rcu_sysidle_exit(int irq)
-{
-}
-
-static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
-				  unsigned long *maxj)
-{
-}
-
-static bool is_sysidle_rcu_state(struct rcu_state *rsp)
-{
-	return false;
-}
-
-static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
-				  unsigned long maxj)
-{
-}
-
-static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
-{
-}
-
-#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
-
 /*
  * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
  * grace-period kthread will do force_quiescent_state() processing?
@@ -3016,13 +2593,7 @@ static void rcu_bind_gp_kthread(void)
 
 	if (!tick_nohz_full_enabled())
 		return;
-#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
-	cpu = tick_do_timer_cpu;
-	if (cpu >= 0 && cpu < nr_cpu_ids)
-		set_cpus_allowed_ptr(current, cpumask_of(cpu));
-#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
 	housekeeping_affine(current);
-#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
 }
 
 /* Record the current task on dyntick-idle entry. */