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@xxxxxxxxx>
---
kernel/rcu/tree.c | 32 ++++++++++++++++++++++++++++++--
kernel/rcu/tree.h | 6 ++++++
2 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index dcc1764e8fad..063200613444 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1672,7 +1672,8 @@ static void rcu_sr_normal_gp_cleanup_work(struct work_struct *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)
@@ -1680,12 +1681,39 @@ 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);
- schedule_work(&rcu_state.srs_cleanup_work);
+ if (wait_tail->next)
+ schedule_work(&rcu_state.srs_cleanup_work);
}
/*
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index b942b9437438..2832787cee1d 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -315,6 +315,12 @@ 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
