From: Frederic Weisbecker <frederic@kernel.org>
To: Ankur Arora <ankur.a.arora@oracle.com>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
tglx@linutronix.de, paulmck@kernel.org, mingo@kernel.org,
bigeasy@linutronix.de, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
vschneid@redhat.com, efault@gmx.de, sshegde@linux.ibm.com,
boris.ostrovsky@oracle.com
Subject: Re: [PATCH v3 5/7] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y
Date: Fri, 13 Dec 2024 14:59:37 +0100 [thread overview]
Message-ID: <Z1w9ydTN90Sl8qda@localhost.localdomain> (raw)
In-Reply-To: <20241213040658.2282640-6-ankur.a.arora@oracle.com>
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>
next prev parent reply other threads:[~2024-12-13 13:59 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-12-13 4:06 [PATCH v3 0/7] RCU changes for PREEMPT_LAZY Ankur Arora
2024-12-13 4:06 ` [PATCH v3 1/7] rcu: fix header guard for rcu_all_qs() Ankur Arora
2024-12-13 4:06 ` [PATCH v3 2/7] rcu: rename PREEMPT_AUTO to PREEMPT_LAZY Ankur Arora
2024-12-13 4:06 ` [PATCH v3 3/7] sched: update __cond_resched comment about RCU quiescent states Ankur Arora
2024-12-13 13:21 ` Frederic Weisbecker
2024-12-13 4:06 ` [PATCH v3 4/7] rcu: handle unstable rdp in rcu_read_unlock_strict() Ankur Arora
2024-12-13 13:38 ` Frederic Weisbecker
2024-12-13 4:06 ` [PATCH v3 5/7] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y Ankur Arora
2024-12-13 13:59 ` Frederic Weisbecker [this message]
2024-12-13 20:44 ` Ankur Arora
2024-12-13 4:06 ` [PATCH v3 6/7] osnoise: provide quiescent states Ankur Arora
2024-12-13 14:34 ` Frederic Weisbecker
2024-12-13 4:06 ` [PATCH v3 7/7] rcu: limit PREEMPT_RCU configurations Ankur Arora
2025-01-08 1:14 ` [PATCH v3 0/7] RCU changes for PREEMPT_LAZY Paul E. McKenney
2025-01-08 18:18 ` Ankur Arora
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