From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
To: "Paul E . McKenney" <paulmck@kernel.org>
Cc: RCU <rcu@vger.kernel.org>,
Neeraj upadhyay <Neeraj.Upadhyay@amd.com>,
Boqun Feng <boqun.feng@gmail.com>,
Hillf Danton <hdanton@sina.com>,
Joel Fernandes <joel@joelfernandes.org>,
LKML <linux-kernel@vger.kernel.org>,
Uladzislau Rezki <urezki@gmail.com>,
Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>,
Frederic Weisbecker <frederic@kernel.org>
Subject: [PATCH v4 4/4] rcu: Support direct wake-up of synchronize_rcu() users
Date: Thu, 4 Jan 2024 17:25:10 +0100 [thread overview]
Message-ID: <20240104162510.72773-5-urezki@gmail.com> (raw)
In-Reply-To: <20240104162510.72773-1-urezki@gmail.com>
This patch introduces a small enhancement which allows to do a
direct wake-up of synchronize_rcu() callers. It occurs after a
completion of grace period, thus by the gp-kthread.
Number of clients is limited by the hard-coded maximum allowed
threshold. The remaining part, if still exists is deferred to
a main worker.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
kernel/rcu/tree.c | 31 +++++++++++++++++++++++++++++--
kernel/rcu/tree.h | 6 ++++++
2 files changed, 35 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 88a47a6a658e..96fe9cc122ca 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1642,7 +1642,8 @@ static DECLARE_WORK(sr_normal_gp_cleanup, rcu_sr_normal_gp_cleanup_work);
*/
static void rcu_sr_normal_gp_cleanup(void)
{
- struct llist_node *wait_tail;
+ struct llist_node *wait_tail, *next, *rcu;
+ int done = 0;
wait_tail = rcu_state.srs_wait_tail;
if (wait_tail == NULL)
@@ -1650,12 +1651,38 @@ static void rcu_sr_normal_gp_cleanup(void)
rcu_state.srs_wait_tail = NULL;
ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_wait_tail);
+ WARN_ON_ONCE(!rcu_sr_is_wait_head(wait_tail));
+
+ /*
+ * Process (a) and (d) cases. See an illustration. Apart of
+ * that it handles the scenario when all clients are done,
+ * wait-head is released if last. The worker is not kicked.
+ */
+ llist_for_each_safe(rcu, next, wait_tail->next) {
+ if (rcu_sr_is_wait_head(rcu)) {
+ if (!rcu->next) {
+ rcu_sr_put_wait_head(rcu);
+ wait_tail->next = NULL;
+ } else {
+ wait_tail->next = rcu;
+ }
+
+ break;
+ }
+
+ rcu_sr_normal_complete(rcu);
+ // It can be last, update a next on this step.
+ wait_tail->next = next;
+
+ if (++done == SR_MAX_USERS_WAKE_FROM_GP)
+ break;
+ }
// concurrent sr_normal_gp_cleanup work might observe this update.
smp_store_release(&rcu_state.srs_done_tail, wait_tail);
ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_done_tail);
- if (wait_tail)
+ if (wait_tail->next)
queue_work(system_highpri_wq, &sr_normal_gp_cleanup);
}
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 4c35d7d37647..5d8b71a1caec 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -316,6 +316,12 @@ do { \
__set_current_state(TASK_RUNNING); \
} while (0)
+/*
+ * A max threshold for synchronize_rcu() users which are
+ * awaken directly by the rcu_gp_kthread(). Left part is
+ * deferred to the main worker.
+ */
+#define SR_MAX_USERS_WAKE_FROM_GP 5
#define SR_NORMAL_GP_WAIT_HEAD_MAX 5
struct sr_wait_node {
--
2.39.2
next prev parent reply other threads:[~2024-01-04 16:25 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-04 16:25 [PATCH v4 0/4] Reduce synchronize_rcu() latency(v4) Uladzislau Rezki (Sony)
2024-01-04 16:25 ` [PATCH v4 1/4] rcu: Reduce synchronize_rcu() latency Uladzislau Rezki (Sony)
2024-01-09 19:16 ` Kalesh Singh
2024-01-10 9:21 ` Uladzislau Rezki
2024-01-11 16:37 ` Kalesh Singh
2024-01-11 17:35 ` Uladzislau Rezki
2024-01-12 23:09 ` Frederic Weisbecker
2024-01-18 10:37 ` Uladzislau Rezki
2024-01-16 16:18 ` Paul E. McKenney
2024-01-17 12:26 ` Uladzislau Rezki
2024-01-19 15:24 ` Paul E. McKenney
2024-01-22 17:35 ` Uladzislau Rezki
2024-01-23 11:21 ` Paul E. McKenney
2024-01-04 16:25 ` [PATCH v4 2/4] rcu: Add a trace event for synchronize_rcu_normal() Uladzislau Rezki (Sony)
2024-01-12 23:20 ` Frederic Weisbecker
2024-01-15 12:14 ` Uladzislau Rezki
2024-01-04 16:25 ` [PATCH v4 3/4] rcu: Improve handling of synchronize_rcu() users Uladzislau Rezki (Sony)
2024-01-16 16:32 ` Paul E. McKenney
2024-01-04 16:25 ` Uladzislau Rezki (Sony) [this message]
2024-01-13 9:19 ` [PATCH v4 4/4] rcu: Support direct wake-up " Z qiang
2024-01-15 10:46 ` Uladzislau Rezki
2024-01-15 10:57 ` Uladzislau Rezki
2024-01-16 6:19 ` Z qiang
2024-01-27 7:07 ` [PATCH v4 0/4] Reduce synchronize_rcu() latency(v4) Paul E. McKenney
2024-01-29 16:23 ` Uladzislau Rezki
2024-01-29 19:43 ` Paul E. McKenney
2024-01-29 20:36 ` Uladzislau Rezki
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