Commit a554ba28 authored Oct 19, 2021 by Frederic Weisbecker Committed by Paul E. McKenney Dec 07, 2021

rcu: Apply callbacks processing time limit only on softirq



Time limit only makes sense when callbacks are serviced in softirq mode
because:

_ In case we need to get back to the scheduler,
  cond_resched_tasks_rcu_qs() is called after each callback.

_ In case some other softirq vector needs the CPU, the call to
  local_bh_enable() before cond_resched_tasks_rcu_qs() takes care about
  them via a call to do_softirq().

Therefore, make sure the time limit only applies to softirq mode.

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 3e61e95e

kernel/rcu/tree.c

+12 −13

Original line number	Diff line number	Diff line
		@@ -2488,7 +2488,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
		div = READ_ONCE(rcu_divisor);
		div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div;
		bl = max(rdp->blimit, pending >> div);
		if (unlikely(bl > 100)) {
		if (in_serving_softirq() && unlikely(bl > 100)) {
		long rrn = READ_ONCE(rcu_resched_ns);

		rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn;
		@@ -2528,14 +2528,6 @@ static void rcu_do_batch(struct rcu_data *rdp)
		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.
		@@ -2547,6 +2539,13 @@ static void rcu_do_batch(struct rcu_data *rdp)
		/* Exceeded the time limit, so leave. */
		break;
		}
		} else {
		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);