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rcu/nocb: Enable re-awakening under high callback load

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The __call_rcu_nocb_wake() function and its predecessors set
->qlen_last_fqs_check to zero for the first callback and to LONG_MAX / 2
for forced reawakenings.  The former can result in a too-quick reawakening
when there are many callbacks ready to invoke and the latter prevents a
second reawakening.  This commit therefore sets ->qlen_last_fqs_check
to the current number of callbacks in both cases.  While in the area,
this commit also moves both assignments under ->nocb_lock.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-05-23 10:43:58 -07:00
parent 0bd55c6936
commit aeeacd9d84
1 changed files with 2 additions and 2 deletions
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4
kernel/rcu/tree_plugin.h
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@ -1628,6 +1628,7 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
// Need to actually to a wakeup.
len = rcu_segcblist_n_cbs(&rdp->cblist);
if (was_alldone) {
rdp->qlen_last_fqs_check = len;
if (!irqs_disabled_flags(flags)) {
/* ... if queue was empty ... */
wake_nocb_gp(rdp, false, flags);
@ -1638,9 +1639,9 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
TPS("WakeEmptyIsDeferred"));
rcu_nocb_unlock_irqrestore(rdp, flags);
}
rdp->qlen_last_fqs_check = 0;
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
/* ... or if many callbacks queued. */
rdp->qlen_last_fqs_check = len;
if (!irqs_disabled_flags(flags)) {
wake_nocb_gp(rdp, true, flags);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
@ -1650,7 +1651,6 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
TPS("WakeOvfIsDeferred"));
rcu_nocb_unlock_irqrestore(rdp, flags);
}
rdp->qlen_last_fqs_check = LONG_MAX / 2;
} else {
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
rcu_nocb_unlock_irqrestore(rdp, flags);