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Commit 663e1310 authored by Paul E. McKenney's avatar Paul E. McKenney
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rcu: 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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Tested-by: default avatarPaul Gortmaker <paul.gortmaker@windriver.com>
parent 417e8d26

kernel/rcu/tree_plugin.h

+18 −1
Original line number Diff line number Diff line
@@ -2707,6 +2707,10 @@ 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--;
@@ -2772,6 +2776,10 @@ 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++;
@@ -2826,6 +2834,10 @@ 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
@@ -2952,6 +2964,10 @@ 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);

}
@@ -2978,7 +2994,8 @@ 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)

{