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osnoise: provide quiescent states

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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>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
This commit is contained in:
Ankur Arora
2024-12-12 20:06:57 -08:00
committed by Boqun Feng
parent 83b28cfe79
commit 9fd858cc5a
1 changed files with 15 additions and 17 deletions
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32
kernel/trace/trace_osnoise.c
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@@ -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