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Subject[PATCH RFC tip/core/rcu 05/14] rcu/nocb: Avoid synchronous wakeup in __call_rcu_nocb_wake()
Date
When callbacks are in full flow, the common case is waiting for a
grace period, and this grace period will normally take a few jiffies to
complete. It therefore isn't all that helpful for __call_rcu_nocb_wake()
to do a synchronous wakeup in this case. This commit therefore turns this
into a timer-based deferred wakeup of the no-CBs grace-period kthread.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
kernel/rcu/tree_plugin.h | 19 +++++--------------
1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index aaeb8a658f4b..5db39ce1cae1 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1897,22 +1897,13 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
/* ... or if many callbacks queued. */
rdp->qlen_last_fqs_check = len;
- if (!rdp->nocb_cb_sleep &&
- rcu_segcblist_ready_cbs(&rdp->cblist)) {
- // Already going full tilt, so don't try to rewake.
- rcu_nocb_unlock_irqrestore(rdp, flags);
- } else {
+ if (rdp->nocb_cb_sleep ||
+ !rcu_segcblist_ready_cbs(&rdp->cblist)) {
rcu_advance_cbs_nowake(rdp->mynode, rdp);
- if (!irqs_disabled_flags(flags)) {
- wake_nocb_gp(rdp, false, flags);
- trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
- TPS("WakeOvf"));
- } else {
- wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
- TPS("WakeOvfIsDeferred"));
- rcu_nocb_unlock_irqrestore(rdp, flags);
- }
+ wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
+ TPS("WakeOvfIsDeferred"));
}
+ rcu_nocb_unlock_irqrestore(rdp, flags);
} else {
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
rcu_nocb_unlock_irqrestore(rdp, flags);
--
2.17.1
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