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rcu: Apply callbacks processing time limit only on softirq 

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2065994

commit a554ba288845fd3f6f12311fd76a51694233458a
Author: Frederic Weisbecker <frederic@kernel.org>
Date:   Tue, 19 Oct 2021 02:08:15 +0200

    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>

Signed-off-by: Waiman Long <longman@redhat.com>
This commit is contained in:
Waiman Long 2022-03-24 17:16:03 -04:00
parent fb8f304925
commit 27dd5723e4
1 changed files with 12 additions and 13 deletions
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25
kernel/rcu/tree.c
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@ -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;
@ -2528,6 +2528,17 @@ static void rcu_do_batch(struct rcu_data *rdp)
if (in_serving_softirq()) {
if (count >= bl && (need_resched() || !is_idle_task(current)))
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((count & 31) || local_clock() < tlimit))
continue;
/* Exceeded the time limit, so leave. */
break;
}
} else {
local_bh_enable();
lockdep_assert_irqs_enabled();
@ -2535,18 +2546,6 @@ 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((count & 31) || local_clock() < tlimit))
continue;
/* Exceeded the time limit, so leave. */
break;
}
}
rcu_nocb_lock_irqsave(rdp, flags);