From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
"Paul E. McKenney" <paulmck@linux.ibm.com>
Subject: [PATCH tip/core/rcu 01/10] rcu/nocb: Enable re-awakening under high callback load
Date: Thu, 1 Aug 2019 16:16:26 -0700 [thread overview]
Message-ID: <20190801231636.23115-1-paulmck@linux.ibm.com> (raw)
In-Reply-To: <20190801231619.GA22610@linux.ibm.com>
The __call_rcu_nocb_wake() function and its predecessors set
->qlen_last_fqs_check to zero for the first callback and to LONG_MAX / 2
for forced reawakenings. The former can result in a too-quick reawakening
when there are many callbacks ready to invoke and the latter prevents a
second reawakening. This commit therefore sets ->qlen_last_fqs_check
to the current number of callbacks in both cases. While in the area,
this commit also moves both assignments under ->nocb_lock.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
kernel/rcu/tree_plugin.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c1dfbac8cd39..297b38732e28 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1626,6 +1626,7 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
// Need to actually to a wakeup.
len = rcu_segcblist_n_cbs(&rdp->cblist);
if (was_alldone) {
+ rdp->qlen_last_fqs_check = len;
if (!irqs_disabled_flags(flags)) {
/* ... if queue was empty ... */
wake_nocb_gp(rdp, false, flags);
@@ -1636,9 +1637,9 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
TPS("WakeEmptyIsDeferred"));
rcu_nocb_unlock_irqrestore(rdp, flags);
}
- rdp->qlen_last_fqs_check = 0;
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
/* ... or if many callbacks queued. */
+ rdp->qlen_last_fqs_check = len;
if (!irqs_disabled_flags(flags)) {
wake_nocb_gp(rdp, true, flags);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
@@ -1648,7 +1649,6 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
TPS("WakeOvfIsDeferred"));
rcu_nocb_unlock_irqrestore(rdp, flags);
}
- rdp->qlen_last_fqs_check = LONG_MAX / 2;
} else {
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
rcu_nocb_unlock_irqrestore(rdp, flags);
--
2.17.1
next prev parent reply other threads:[~2019-08-01 23:16 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-01 23:16 [PATCH tip/core/rcu 0/10] No-CBs contention-reduction updates for v5.3-rc2 Paul E. McKenney
2019-08-01 23:16 ` Paul E. McKenney [this message]
2019-08-01 23:16 ` [PATCH tip/core/rcu 02/10] rcu/nocb: Never downgrade ->nocb_defer_wakeup in wake_nocb_gp_defer() Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 03/10] rcu/nocb: Make __call_rcu_nocb_wake() safe for many callbacks Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 04/10] rcu/nocb: Avoid needless wakeups of no-CBs grace-period kthread Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 05/10] rcu/nocb: Avoid ->nocb_lock capture by corresponding CPU Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 06/10] rcu/nocb: Round down for number of no-CBs grace-period kthreads Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 07/10] rcu/nocb: Reduce contention at no-CBs registry-time CB advancement Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 08/10] rcu/nocb: Reduce contention at no-CBs invocation-done time Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 09/10] rcu/nocb: Reduce ->nocb_lock contention with separate ->nocb_gp_lock Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 10/10] rcu/nocb: Unconditionally advance and wake for excessive CBs Paul E. McKenney
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