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rcu: Support direct wake-up of synchronize_rcu() users

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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.

Link: https://lore.kernel.org/lkml/Zd0ZtNu+Rt0qXkfS@lothringen/

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
This commit is contained in:
Uladzislau Rezki (Sony) 2024-03-08 18:34:07 +01:00
parent 2053937a31
commit 462df2f543
2 changed files with 29 additions and 1 deletions
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24
kernel/rcu/tree.c
View File

@ -1645,7 +1645,8 @@ 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)
@ -1653,11 +1654,32 @@ 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.
*/
llist_for_each_safe(rcu, next, wait_tail->next) {
if (rcu_sr_is_wait_head(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);
/*
* We schedule a work in order to perform a final processing
* of outstanding users(if still left) and releasing wait-heads
* added by rcu_sr_normal_gp_init() call.
*/
schedule_work(&rcu_state.srs_cleanup_work);
}

6
kernel/rcu/tree.h
View File

@ -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 {