Commit-ID: ba1c64c27239373be1b3d88cf0a9ac1b10fa871f
Gitweb: https://git.kernel.org/tip/ba1c64c27239373be1b3d88cf0a9ac1b10fa871f
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Sat, 30 Jun 2018 15:23:37 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Thu, 30 Aug 2018 16:02:38 -0700
rcu: Report expedited grace periods at context-switch time
This commit reduces the latency of expedited RCU grace periods by
reporting a quiescent state for the CPU at context-switch time.
In CONFIG_PREEMPT=y kernels, if the outgoing task is still within an
RCU read-side critical section (and thus still blocking some grace
period, perhaps including this expedited grace period), then that task
will already have been placed on one of the leaf rcu_node structures'
->blkd_tasks list.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree_plugin.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c686bf63bba5..0d7107fb3dec 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -332,7 +332,7 @@ static void rcu_preempt_qs(void)
static void rcu_preempt_note_context_switch(bool preempt)
{
struct task_struct *t = current;
- struct rcu_data *rdp;
+ struct rcu_data *rdp = this_cpu_ptr(rcu_state_p->rda);
struct rcu_node *rnp;
lockdep_assert_irqs_disabled();
@@ -341,7 +341,6 @@ static void rcu_preempt_note_context_switch(bool preempt)
!t->rcu_read_unlock_special.b.blocked) {
/* Possibly blocking in an RCU read-side critical section. */
- rdp = this_cpu_ptr(rcu_state_p->rda);
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp);
t->rcu_read_unlock_special.b.blocked = true;
@@ -383,6 +382,8 @@ static void rcu_preempt_note_context_switch(bool preempt)
* means that we continue to block the current grace period.
*/
rcu_preempt_qs();
+ if (rdp->deferred_qs)
+ rcu_report_exp_rdp(rcu_state_p, rdp, true);
}
/*
|