[PATCH] rcu-tasks: Stop RCU Tasks scanning tasks which record on dyntick-idle entry

Zqiang
2022-05-20T04:56:51Z

When the RCU Tasks scanning on-rq tasks, there is no need to scanning
tasks which record on dyntick-idle entry, at this time, these tasks are
not remain within an RCU Tasks read-side critical section.

This commit skip scanning tasks which record on dyntick-idle entry in
rcu_tasks_pertask().

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
---
kernel/rcu/tasks.h | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index f6459343e4b6..7898da987581 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -206,6 +206,12 @@ static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate)
rtp->gp_jiffies = jiffies;
}

+static bool task_is_on_dyntick_idle(struct task_struct *t)
+{
+ return IS_ENABLED(CONFIG_NO_HZ_FULL) && !is_idle_task(t) &&
+ t->rcu_tasks_idle_cpu >= 0;
+}
+
#ifndef CONFIG_TINY_RCU
/* Return state name. */
static const char *tasks_gp_state_getname(struct rcu_tasks *rtp)
@@ -812,7 +818,8 @@ static void rcu_tasks_pregp_step(struct list_head *hop)
/* Per-task initial processing. */
static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)
{
- if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {
+ if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t) &&
+ !task_is_on_dyntick_idle(t)) {
get_task_struct(t);
t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
WRITE_ONCE(t->rcu_tasks_holdout, true);
@@ -842,8 +849,7 @@ static void check_holdout_task(struct task_struct *t,
if (!READ_ONCE(t->rcu_tasks_holdout) ||
t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
!READ_ONCE(t->on_rq) ||
- (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
- !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
+ task_is_on_dyntick_idle(t)) {
WRITE_ONCE(t->rcu_tasks_holdout, false);
list_del_init(&t->rcu_tasks_holdout_list);
put_task_struct(t);
--
2.25.1