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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@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-06-30 15:23:37 -07:00
parent d28139c4e9
commit ba1c64c272
1 changed files with 3 additions and 2 deletions
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5
kernel/rcu/tree_plugin.h
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@ -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);
}
/*