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rcu/nocb: Prepare for fine-grained deferred wakeup

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Tuning the deferred wakeup level must be done from a safe wakeup
point. Currently those sites are:

* ->nocb_timer
* user/idle/guest entry
* CPU down
* softirq/rcuc

All of these sites perform the wake up for both RCU_NOCB_WAKE and
RCU_NOCB_WAKE_FORCE.

In order to merge ->nocb_timer and ->nocb_bypass_timer together, we plan
to add a new RCU_NOCB_WAKE_BYPASS that really should be deferred until
a timer fires so that we don't wake up the NOCB-gp kthread too early.

To prepare for that, this commit specifies the per-callsite wakeup
level/limit.

Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
[ paulmck: Fix non-NOCB rcu_nocb_need_deferred_wakeup() definition. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Frederic Weisbecker 2021-02-23 01:10:10 +01:00 committed by Paul E. McKenney
parent f9fc166b79
commit 870905169d
3 changed files with 11 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
kernel/rcu/tree.c
View file

@ -3911,7 +3911,7 @@ static int rcu_pending(int user)
check_cpu_stall(rdp);
/* Does this CPU need a deferred NOCB wakeup? */
if (rcu_nocb_need_deferred_wakeup(rdp))
if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE))
return 1;
/* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */

2
kernel/rcu/tree.h
View file

@ -433,7 +433,7 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
bool *was_alldone, unsigned long flags);
static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
unsigned long flags);
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp);
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level);
static bool do_nocb_deferred_wakeup(struct rcu_data *rdp);
static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
static void rcu_spawn_cpu_nocb_kthread(int cpu);

17
kernel/rcu/tree_plugin.h
View file

@ -2352,13 +2352,14 @@ static int rcu_nocb_cb_kthread(void *arg)
}
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
{
return READ_ONCE(rdp->nocb_defer_wakeup) > RCU_NOCB_WAKE_NOT;
return READ_ONCE(rdp->nocb_defer_wakeup) >= level;
}
/* Do a deferred wakeup of rcu_nocb_kthread(). */
static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp,
int level)
{
unsigned long flags;
int ndw;
@ -2367,7 +2368,7 @@ static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
if (!rcu_nocb_need_deferred_wakeup(rdp_gp)) {
if (!rcu_nocb_need_deferred_wakeup(rdp_gp, level)) {
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
return false;
}
@ -2384,7 +2385,7 @@ static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
{
struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
do_nocb_deferred_wakeup_common(rdp);
do_nocb_deferred_wakeup_common(rdp, RCU_NOCB_WAKE);
}
/*
@ -2397,8 +2398,8 @@ static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
if (!rdp->nocb_gp_rdp)
return false;
if (rcu_nocb_need_deferred_wakeup(rdp->nocb_gp_rdp))
return do_nocb_deferred_wakeup_common(rdp);
if (rcu_nocb_need_deferred_wakeup(rdp->nocb_gp_rdp, RCU_NOCB_WAKE))
return do_nocb_deferred_wakeup_common(rdp, RCU_NOCB_WAKE);
return false;
}
@ -2939,7 +2940,7 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
}
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
{
return false;
}