Re: [PATCH v3 5/7] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y

[Ankur Arora <ankur.a.arora@oracle.com>]

Frederic Weisbecker <frederic@kernel.org> writes:

> Le Thu, Dec 12, 2024 at 08:06:56PM -0800, Ankur Arora a écrit :
>> With PREEMPT_RCU=n, cond_resched() provides urgently needed quiescent
>> states for read-side critical sections via rcu_all_qs().
>> One reason why this was needed: lacking preempt-count, the tick
>> handler has no way of knowing whether it is executing in a
>> read-side critical section or not.
>>
>> With (PREEMPT_LAZY=y, PREEMPT_DYNAMIC=n), we get (PREEMPT_COUNT=y,
>> PREEMPT_RCU=n). In this configuration cond_resched() is a stub and
>> does not provide quiescent states via rcu_all_qs().
>> (PREEMPT_RCU=y provides this information via rcu_read_unlock() and
>> its nesting counter.)
>>
>> So, use the availability of preempt_count() to report quiescent states
>> in rcu_flavor_sched_clock_irq().
>>
>> Suggested-by: Paul E. McKenney <paulmck@kernel.org>
>> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>
> Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

Thanks for all the reviews!

--
ankur