Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 10/11] rcu: Apply callbacks processing time limit only on softirq | Date | Mon, 11 Oct 2021 16:51:39 +0200 |
| |
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> --- kernel/rcu/tree.c | 25 ++++++++++++------------- 1 file changed, 12 insertions(+), 13 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 7a655d93a28a..0ca4f4ec724d 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2498,7 +2498,7 @@ 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; @@ -2538,6 +2538,17 @@ 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(); @@ -2545,18 +2556,6 @@ 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); -- 2.25.1
| |