From 870905169da8bfae0570df013efe860d33251b0f Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Tue, 23 Feb 2021 01:10:10 +0100 Subject: [PATCH] rcu/nocb: Prepare for fine-grained deferred wakeup 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 Cc: Lai Jiangshan Cc: Joel Fernandes Cc: Neeraj Upadhyay Cc: Boqun Feng Signed-off-by: Frederic Weisbecker [ paulmck: Fix non-NOCB rcu_nocb_need_deferred_wakeup() definition. ] Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 2 +- kernel/rcu/tree.h | 2 +- kernel/rcu/tree_plugin.h | 17 +++++++++-------- 3 files changed, 11 insertions(+), 10 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 8e78b2430c16..5f1545aab9ed 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -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.) */ 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 db28e3123f32..e2e5e4968f43 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -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; } -- 2.20.1