Commit 3e61e95e authored Oct 19, 2021 by Frederic Weisbecker Committed by Paul E. McKenney Dec 07, 2021

rcu: Fix callbacks processing time limit retaining cond_resched()



The callbacks processing time limit makes sure we are not exceeding a
given amount of time executing the queue.

However its "continue" clause bypasses the cond_resched() call on
rcuc and NOCB kthreads, delaying it until we reach the limit, which can
be very long...

Make sure the scheduler has a higher priority than the time limit.

Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

parent 78ad37a2

kernel/rcu/tree.c

+15 −10

Original line number	Diff line number	Diff line
		@@ -2525,9 +2525,21 @@ static void rcu_do_batch(struct rcu_data *rdp)
		/*
		* Stop only if limit reached and CPU has something to do.
		*/
		if (count >= bl && in_serving_softirq() &&
		(need_resched() \|\| !is_idle_task(current)))
		if (in_serving_softirq()) {
		if (count >= bl && (need_resched() \|\| !is_idle_task(current)))
		break;
		} else {
		local_bh_enable();
		lockdep_assert_irqs_enabled();
		cond_resched_tasks_rcu_qs();
		lockdep_assert_irqs_enabled();
		local_bh_disable();
		}

		/*
		* Make sure we don't spend too much time here and deprive other
		* softirq vectors of CPU cycles.
		*/
		if (unlikely(tlimit)) {
		/* only call local_clock() every 32 callbacks */
		if (likely((count & 31) \|\| local_clock() < tlimit))
		@@ -2535,13 +2547,6 @@ static void rcu_do_batch(struct rcu_data *rdp)
		/* Exceeded the time limit, so leave. */
		break;
		}
		if (!in_serving_softirq()) {
		local_bh_enable();
		lockdep_assert_irqs_enabled();
		cond_resched_tasks_rcu_qs();
		lockdep_assert_irqs_enabled();
		local_bh_disable();
		}
		}

		rcu_nocb_lock_irqsave(rdp, flags);