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rcu/nocb: Avoid synchronous wakeup in __call_rcu_nocb_wake() 

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>
This commit is contained in:
Paul E. McKenney 2019-07-09 06:54:42 -07:00
parent f7a81b12d6
commit 273f034065
1 changed files with 5 additions and 14 deletions
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19
kernel/rcu/tree_plugin.h
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@ -1900,22 +1900,13 @@ 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);