From: Ankur Arora ankur.a.arora@oracle.com
To reduce RCU noise for nohz_full configurations, osnoise depends on cond_resched() providing quiescent states for PREEMPT_RCU=n configurations. For PREEMPT_RCU=y configurations -- where cond_resched() is a stub -- we do this by directly calling rcu_momentary_eqs().
With (PREEMPT_LAZY=y, PREEMPT_DYNAMIC=n), however, we have a configuration with (PREEMPTION=y, PREEMPT_RCU=n) where neither of the above can help.
Handle that by providing an explicit quiescent state here for all configurations.
As mentioned above this is not needed for non-stubbed cond_resched(), but, providing a quiescent state here just pulls in one that a future cond_resched() would provide, so doesn't cause any extra work for this configuration.
Cc: Paul E. McKenney paulmck@kernel.org Cc: Daniel Bristot de Oliveira bristot@kernel.org Cc: Steven Rostedt rostedt@goodmis.org Suggested-by: Paul E. McKenney paulmck@kernel.org Acked-by: Daniel Bristot de Oliveira bristot@kernel.org Signed-off-by: Ankur Arora ankur.a.arora@oracle.com Reviewed-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Boqun Feng boqun.feng@gmail.com --- kernel/trace/trace_osnoise.c | 32 +++++++++++++++----------------- 1 file changed, 15 insertions(+), 17 deletions(-)
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index f3a2722ee4c0..512034e365ad 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -1542,27 +1542,25 @@ 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_eqs(), 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. + * a stopped tick PREEMPT_RCU or PREEMPT_LAZY have 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 by calling + * rcu_momentary_eqs(), 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. * - * Note that in non PREEMPT_RCU kernels QSs are handled through - * cond_resched() + * Normally QSs for other cases are handled through cond_resched(). + * For simplicity, however, we call rcu_momentary_eqs() for all + * configurations here. */ - if (IS_ENABLED(CONFIG_PREEMPT_RCU)) { - if (!disable_irq) - local_irq_disable(); + if (!disable_irq) + local_irq_disable();
- rcu_momentary_eqs(); + rcu_momentary_eqs();
- if (!disable_irq) - local_irq_enable(); - } + if (!disable_irq) + local_irq_enable();
/* * For the non-preemptive kernel config: let threads runs, if