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rcu/nocb: Unconditionally advance and wake for excessive CBs

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When there are excessive numbers of callbacks, and when either the
corresponding no-CBs callback kthread is asleep or there is no more
ready-to-invoke callbacks, and when least one callback is pending,
__call_rcu_nocb_wake() will advance the callbacks, but refrain from
awakening the corresponding no-CBs grace-period kthread.  However,
because rcu_advance_cbs_nowake() is used, it is possible (if a bit
unlikely) that the needed advancement could not happen due to a grace
period not being in progress.  Plus there will always be at least one
pending callback due to one having just now been enqueued.

This commit therefore attempts to advance callbacks and awakens the
no-CBs grace-period kthread when there are excessive numbers of callbacks
posted and when the no-CBs callback kthread is not in a position to do
anything helpful.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-06-26 09:50:38 -07:00
parent 4fd8c5f153
commit faca5c2509
1 changed files with 11 additions and 5 deletions
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16
kernel/rcu/tree_plugin.h
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@ -1668,13 +1668,19 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
if (!rdp->nocb_cb_sleep &&
rcu_segcblist_ready_cbs(&rdp->cblist)) {
// Already going full tilt, so don't try to rewake.
} else if (rcu_segcblist_pend_cbs(&rdp->cblist)) {
rcu_advance_cbs_nowake(rdp->mynode, rdp);
rcu_nocb_unlock_irqrestore(rdp, flags);
} else {
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
TPS("WakeOvfIsDeferred"));
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);
}
}
rcu_nocb_unlock_irqrestore(rdp, flags);
} else {
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
rcu_nocb_unlock_irqrestore(rdp, flags);