lkml.org 
[lkml]   [2021]   [Feb]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 12/13] rcu/nocb: Prepare for finegrained deferred wakeup
Date
Provide a way to tune the deferred wakeup level we want to perform 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 want to be deferred until
a timer fires so that we don't wake up the NOCB-gp kthread too early.

To prepare for that, integrate a wake up level/limit that a callsite is
deemed to perform.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
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>
---
kernel/rcu/tree.c | 2 +-
kernel/rcu/tree.h | 2 +-
kernel/rcu/tree_plugin.h | 15 ++++++++-------
3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2c9cf4df942c..9951a4bef504 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3823,7 +3823,7 @@ 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.) */
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index b280a843bd2c..2510e86265c1 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -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);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index d8b50ff40e4b..e0420e3b30e6 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2364,13 +2364,14 @@ 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;
@@ -2379,7 +2380,7 @@ 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;
}
@@ -2396,7 +2397,7 @@ 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);
}

/*
@@ -2409,8 +2410,8 @@ 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;
}

--
2.25.1
\
 
 \ /
  Last update: 2021-02-23 01:17    [W:0.069 / U:6.256 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site