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McKenney" Subject: [PATCH 2/2] rcu: Apply callbacks processing time limit only on softirq Date: Mon, 2 May 2022 21:08:33 +0200 Message-Id: <20220502190833.3352-3-urezki@gmail.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220502190833.3352-1-urezki@gmail.com> References: <20220502190833.3352-1-urezki@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: Frederic Weisbecker commit a554ba288845fd3f6f12311fd76a51694233458a 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. Fixes: cfcdef5e30469 ("rcu: Allow rcu_do_batch() to dynamically adjust batch sizes") Reviewed-by: Valentin Schneider Tested-by: Valentin Schneider Tested-by: Sebastian Andrzej Siewior Signed-off-by: Frederic Weisbecker Cc: Valentin Schneider Cc: Peter Zijlstra Cc: Sebastian Andrzej Siewior Cc: Josh Triplett Cc: Joel Fernandes Cc: Boqun Feng Cc: Neeraj Upadhyay Cc: Uladzislau Rezki Cc: Thomas Gleixner Cc: Oleksiy Avramchenko [UR: backport to 5.10-stable] Signed-off-by: Paul E. McKenney Signed-off-by: Uladzislau Rezki (Sony) --- kernel/rcu/tree.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f340df6ebd86..b41009a283ca 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -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); -- 2.30.2