To reduce RCU noise for the stopped tick case we introduce explicit
quiescent states for PREEMPT_RCU=y, and depend on cond_resched()
(and thus rcu_all_qs()) to handle PREEMPT_RCU=n.
With cond_resched() going away, introduce explicit quiescent states
for all configurations.
Suggested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
kernel/trace/trace_osnoise.c | 37 ++++++++++++------------------------
1 file changed, 12 insertions(+), 25 deletions(-)
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index bd0d01d00fb9..db38934c4242 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1531,34 +1531,21 @@ static int run_osnoise(void)
/*
* In some cases, notably when running on a nohz_full CPU with
- * a stopped tick PREEMPT_RCU has no way to account for QSs.
- * This will eventually cause unwarranted noise as PREEMPT_RCU
- * will force preemption as the means of ending the current
- * grace period. We avoid this problem by calling
- * rcu_momentary_dyntick_idle(), which performs a zero duration
- * EQS allowing PREEMPT_RCU to end the current grace period.
- * This call shouldn't be wrapped inside an RCU critical
- * section.
- *
- * Note that in non PREEMPT_RCU kernels QSs are handled through
- * cond_resched()
+ * a stopped tick RCU has no way to account for QSs. This will
+ * eventually cause unwarranted noise as RCU forces preemption
+ * as the means of ending the current grace period.
+ * We avoid this problem by calling rcu_momentary_dyntick_idle(),
+ * which performs a zero duration EQS allowing RCU to end the
+ * current grace period. This call shouldn't be wrapped inside
+ * an RCU critical section.
*/
- if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
- if (!disable_irq)
- local_irq_disable();
+ if (!disable_irq)
+ local_irq_disable();
- rcu_momentary_dyntick_idle();
+ rcu_momentary_dyntick_idle();
- if (!disable_irq)
- local_irq_enable();
- }
-
- /*
- * For the non-preemptive kernel config: let threads runs, if
- * they so wish, unless set not do to so.
- */
- if (!disable_irq && !disable_preemption)
- cond_resched();
+ if (!disable_irq)
+ local_irq_enable();
last_sample = sample;
last_int_count = int_count;
--
2.31.1
