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| author | Ankur Arora <ankur.a.arora@oracle.com> | 2024-02-12 21:55:54 -0800 |
|---|---|---|
| committer | Joel Fernandes (Google) <joel@joelfernandes.org> | 2024-03-01 21:01:06 -0500 |
| commit | 7328b23e2b34ad9f210690b0cce2b47eda036e81 (patch) | |
| tree | 7d4e6c706e8cba212343186c0c1738abd4a15291 | |
| parent | 2a21548054515b0381c7b4b0ce7eb58ffc3e74ca (diff) | |
| download | linux-sched/preempt.auto.review.tar.gz | |
osnoise: handle quiescent states for PREEMPT_RCU=n, PREEMPTION=ysched/preempt.auto.review
To reduce RCU noise for nohz_full configurations, osnoise depends
on cond_resched() providing quiescent states for PREEMPT_RCU=n
configurations. And, for PREEMPT_RCU=y configurations does this
by directly calling rcu_momentary_dyntick_idle().
With PREEMPT_AUTO=y, however, we can have configurations with
(PREEMPTION=y, PREEMPT_RCU=n), which means neither of the above can
help.
Handle that by fallback to the explicit quiescent states via
rcu_momentary_dyntick_idle().
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>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
| -rw-r--r-- | kernel/trace/trace_osnoise.c | 22 |
1 files changed, 12 insertions, 10 deletions
diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index a8e28f9b9271cf..88d2cd2593c403 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -1532,18 +1532,20 @@ 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. + * 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_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. * - * Note that in non PREEMPT_RCU kernels QSs are handled through - * cond_resched() + * For non-PREEMPT_RCU kernels with cond_resched() (non- + * PREEMPT_AUTO configurations), QSs are handled through + * cond_resched(). For PREEMPT_AUTO kernels, we fallback to the + * zero duration QS via rcu_momentary_dyntick_idle(). */ - if (IS_ENABLED(CONFIG_PREEMPT_RCU)) { + if (IS_ENABLED(CONFIG_PREEMPT_RCU) || + (!IS_ENABLED(CONFIG_PREEMPT_RCU) && IS_ENABLED(CONFIG_PREEMPTION))) { if (!disable_irq) local_irq_disable(); |