Commit a0eb22bf authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Reduce dyntick-idle state space 



Both extended-quiescent-state entry and exit first update the nesting
counter and then adjust the dyntick-idle state.  This means that there
are four states: (1) Both nesting and dyntick idle indicate idle,
(2) Nesting indicates idle but dyntick idle does not, (3) Nesting indicates
non-idle and dyntick idle does not, and (4) Both nesting and dyntick
idle indicate non-idle.  This commit simplifies the state space by
eliminating #3, reversing the order of updates on exit from extended
quiescent state.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 2e672ab2

kernel/rcu/tree.c

+11 −12
Original line number Diff line number Diff line
@@ -928,21 +928,21 @@ void rcu_irq_exit_irqson(void) 
 * we really have exited idle, and must do the appropriate accounting.

 * The caller must have disabled interrupts.

 */

static void rcu_eqs_exit_common(long long oldval, int user)

static void rcu_eqs_exit_common(long long newval, int user)

{

	RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);)



	rcu_dynticks_task_exit();

	rcu_dynticks_eqs_exit();

	rcu_cleanup_after_idle();

	trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);

	trace_rcu_dyntick(TPS("End"), rdtp->dynticks_nesting, newval);

	if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&

	    !user && !is_idle_task(current)) {

		struct task_struct *idle __maybe_unused =

			idle_task(smp_processor_id());



		trace_rcu_dyntick(TPS("Error on exit: not idle task"),

				  oldval, rdtp->dynticks_nesting);

				  rdtp->dynticks_nesting, newval);

		rcu_ftrace_dump(DUMP_ORIG);

		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",

			  current->pid, current->comm,
@@ -967,8 +967,8 @@ static void rcu_eqs_exit(bool user) 
		rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;

	} else {

		__this_cpu_inc(disable_rcu_irq_enter);

		rcu_eqs_exit_common(DYNTICK_TASK_EXIT_IDLE, user);

		rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;

		rcu_eqs_exit_common(oldval, user);

		__this_cpu_dec(disable_rcu_irq_enter);

	}

}
@@ -1037,7 +1037,7 @@ void rcu_user_exit(void) 
void rcu_irq_enter(void)

{

	struct rcu_dynticks *rdtp;

	long long oldval;

	long long newval;



	lockdep_assert_irqs_disabled();

	rdtp = this_cpu_ptr(&rcu_dynticks);
@@ -1046,14 +1046,13 @@ void rcu_irq_enter(void) 
	if (rdtp->dynticks_nmi_nesting)

		return;



	oldval = rdtp->dynticks_nesting;

	rdtp->dynticks_nesting++;

	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&

		     rdtp->dynticks_nesting == 0);

	if (oldval)

		trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);

	newval = rdtp->dynticks_nesting + 1;

	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && newval == 0);

	if (rdtp->dynticks_nesting)

		trace_rcu_dyntick(TPS("++="), rdtp->dynticks_nesting, newval);

	else

		rcu_eqs_exit_common(oldval, true);

		rcu_eqs_exit_common(newval, true);

	rdtp->dynticks_nesting++;

}



/*

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