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rcu: Apply callbacks processing time limit only on softirq

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commit a554ba2888 upstream.

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>
[UR: backport to 5.10-stable]
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Frederic Weisbecker
2021-10-19 02:08:15 +02:00
committed by Greg Kroah-Hartman
parent 40fb3812d9
commit a22d66eb51
1 changed files with 13 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

26
kernel/rcu/tree.c
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@@ -2456,7 +2456,7 @@ 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;
@@ -2494,6 +2494,18 @@ static void rcu_do_batch(struct rcu_data *rdp)
if (-rcl.len >= bl && (need_resched() ||
(!is_idle_task(current) && !rcu_is_callbacks_kthread())))
break;
/*
* 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((-rcl.len & 31) || local_clock() < tlimit))
continue;
/* Exceeded the time limit, so leave. */
break;
}
} else {
local_bh_enable();
lockdep_assert_irqs_enabled();
@@ -2501,18 +2513,6 @@ static void rcu_do_batch(struct rcu_data *rdp)
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((-rcl.len & 31) || local_clock() < tlimit))
continue;
/* Exceeded the time limit, so leave. */
break;
}
}
local_irq_save(flags);