diff options
| author | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-05-28 05:54:26 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-08-13 14:35:49 -0700 |
| commit | 7f36ef82e5cf0b401c2676fb3e56ad0633ed6ad5 (patch) | |
| tree | 4c71dcb767da7b42feae5f1d159d2a604d829d03 /kernel/rcu/tree_plugin.h | |
| parent | ce0a825e40606d6dbe6dfe90d4d4c0ccc9fa3bde (diff) | |
rcu/nocb: Avoid needless wakeups of no-CBs grace-period kthread
Currently, the code provides an extra wakeup for the no-CBs grace-period
kthread if one of its CPUs is generating excessive numbers of callbacks.
But satisfying though it is to wake something up when things are going
south, unless the thing being awakened can actually help solve the
problem, that extra wakeup does nothing but consume additional CPU time,
which is exactly what you don't want during a call_rcu() flood.
This commit therefore avoids doing anything if the corresponding
no-CBs callback kthread is going full tilt. Otherwise, if advancing
callbacks immediately might help and if the leaf rcu_node structure's
lock is immediately available, this commit invokes a new variant of
rcu_advance_cbs() that advances callbacks only if doing so won't require
awakening the grace-period kthread (not to be confused with any of the
no-CBs grace-period kthreads).
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 5cbc0848647c..c10afe778430 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1643,10 +1643,15 @@ 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 (!irqs_disabled_flags(flags)) { - wake_nocb_gp(rdp, true, flags); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("WakeOvf")); + 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 (rcu_segcblist_pend_cbs(&rdp->cblist) && + raw_spin_trylock_rcu_node(rdp->mynode)) { + rcu_advance_cbs_nowake(rdp->mynode, rdp); + raw_spin_unlock_rcu_node(rdp->mynode); + rcu_nocb_unlock_irqrestore(rdp, flags); } else { wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE, TPS("WakeOvfIsDeferred")); |