> When RCU_BOOST is enabled, the boost kthreads will boosting readers
> who are blocking a given grace period, if the current reader tasks
> have a higher priority than boost kthreads(the boost kthreads priority
> not always 1, if the kthread_prio is set), boosting is useless, skip
> current task and select next task to boosting, reduce the time for a
> given grace period.
>
> Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
> ---
> v1->v2:
> rename label 'end' to 'skip_boost'.
> add 'boost_exp_tasks' pointer to point 'rnp->exp_tasks'
> do the similar thing as normal grace period.
>
> kernel/rcu/tree.h | 2 ++
> kernel/rcu/tree_plugin.h | 31 +++++++++++++++++++++++--------
> 2 files changed, 25 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index
> b8d07bf92d29..862ca09b56c7 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -103,6 +103,8 @@ struct rcu_node {
> /* queued on this rcu_node structure that */
> /* are blocking the current grace period, */
> /* there can be no such task. */
> + struct list_head *boost_exp_tasks;
> +
> struct rt_mutex boost_mtx;
> /* Used only for the priority-boosting */
> /* side effect, not as a lock. */ diff --git
> a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index
> c3d212bc5338..22bf5a8040f5 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -12,6 +12,7 @@
> */
>
> #include "../locking/rtmutex_common.h"
> +#include <linux/sched/deadline.h>
>
> static bool rcu_rdp_is_offloaded(struct rcu_data *rdp) { @@ -535,6
> +536,8 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
> drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t;
> if (&t->rcu_node_entry == rnp->boost_tasks)
> WRITE_ONCE(rnp->boost_tasks, np);
> + if (&t->rcu_node_entry == rnp->boost_exp_tasks)
> + WRITE_ONCE(rnp->boost_exp_tasks, np);
> }
>
> /*
> @@ -1022,7 +1025,7 @@ static int rcu_boost(struct rcu_node *rnp)
> struct task_struct *t;
> struct list_head *tb;
>
> - if (READ_ONCE(rnp->exp_tasks) == NULL &&
> + if (READ_ONCE(rnp->boost_exp_tasks) == NULL &&
> READ_ONCE(rnp->boost_tasks) == NULL)
> return 0; /* Nothing left to boost. */
>
> @@ -1032,7 +1035,7 @@ static int rcu_boost(struct rcu_node *rnp)
> * Recheck under the lock: all tasks in need of boosting
> * might exit their RCU read-side critical sections on their own.
> */
> - if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
> + if (rnp->boost_exp_tasks == NULL && rnp->boost_tasks == NULL) {
> raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> return 0;
> }
> @@ -1043,8 +1046,8 @@ static int rcu_boost(struct rcu_node *rnp)
> * expedited grace period must boost all blocked tasks, including
> * those blocking the pre-existing normal grace period.
> */
> - if (rnp->exp_tasks != NULL)
> - tb = rnp->exp_tasks;
> + if (rnp->boost_exp_tasks != NULL)
> + tb = rnp->boost_exp_tasks;
> else
> tb = rnp->boost_tasks;
>
> @@ -1065,14 +1068,24 @@ static int rcu_boost(struct rcu_node *rnp)
> * section.
> */
> t = container_of(tb, struct task_struct, rcu_node_entry);
> + if (dl_task(t) || t->prio <= current->prio) {
>This is a bit confusing to me. We know that "current" has SCHED_FIFO class. In this scenario if "t->prio" has lower value(higher priority) the task falls into all real-time categories anyway and is either:
> - SCHED_FIFO
> - SCHED_RR
> - SCHED_DEADLINE
>
>Checking whether the task is dl_task() sounds like unnecessary there.
>Am i missing something? Could you please comment on it?
Thanks feedback
Right, the deadline task's prio has lower value than rt fifo/rr task.
dl_task() condition detection seems redundant.
>
>Thanks!
>
>--
>Vlad Rezki
