Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:
 "This cycle's RCU changes were:

   - A few more RCU flavor consolidation cleanups.

   - Updates to RCU's list-traversal macros improving lockdep usability.

   - Forward-progress improvements for no-CBs CPUs: Avoid ignoring
     incoming callbacks during grace-period waits.

   - Forward-progress improvements for no-CBs CPUs: Use ->cblist
     structure to take advantage of others' grace periods.

   - Also added a small commit that avoids needlessly inflicting
     scheduler-clock ticks on callback-offloaded CPUs.

   - Forward-progress improvements for no-CBs CPUs: Reduce contention on
     ->nocb_lock guarding ->cblist.

   - Forward-progress improvements for no-CBs CPUs: Add ->nocb_bypass
     list to further reduce contention on ->nocb_lock guarding ->cblist.

   - Miscellaneous fixes.

   - Torture-test updates.

   - minor LKMM updates"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (86 commits)
  MAINTAINERS: Update from paulmck@linux.ibm.com to paulmck@kernel.org
  rcu: Don't include <linux/ktime.h> in rcutiny.h
  rcu: Allow rcu_do_batch() to dynamically adjust batch sizes
  rcu/nocb: Don't wake no-CBs GP kthread if timer posted under overload
  rcu/nocb: Reduce __call_rcu_nocb_wake() leaf rcu_node ->lock contention
  rcu/nocb: Reduce nocb_cb_wait() leaf rcu_node ->lock contention
  rcu/nocb: Advance CBs after merge in rcutree_migrate_callbacks()
  rcu/nocb: Avoid synchronous wakeup in __call_rcu_nocb_wake()
  rcu/nocb: Print no-CBs diagnostics when rcutorture writer unduly delayed
  rcu/nocb: EXP Check use and usefulness of ->nocb_lock_contended
  rcu/nocb: Add bypass callback queueing
  rcu/nocb: Atomic ->len field in rcu_segcblist structure
  rcu/nocb: Unconditionally advance and wake for excessive CBs
  rcu/nocb: Reduce ->nocb_lock contention with separate ->nocb_gp_lock
  rcu/nocb: Reduce contention at no-CBs invocation-done time
  rcu/nocb: Reduce contention at no-CBs registry-time CB advancement
  rcu/nocb: Round down for number of no-CBs grace-period kthreads
  rcu/nocb: Avoid ->nocb_lock capture by corresponding CPU
  rcu/nocb: Avoid needless wakeups of no-CBs grace-period kthread
  rcu/nocb: Make __call_rcu_nocb_wake() safe for many callbacks
  ...

1 files changed, 52 insertions, 29 deletions

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 7acaf3a62d39..c612f306fe89 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -194,29 +194,38 @@ struct rcu_data {
 
 	/* 5) Callback offloading. */
 #ifdef CONFIG_RCU_NOCB_CPU
-	struct rcu_head *nocb_head;	/* CBs waiting for kthread. */
-	struct rcu_head **nocb_tail;
-	atomic_long_t nocb_q_count;	/* # CBs waiting for nocb */
-	atomic_long_t nocb_q_count_lazy; /*  invocation (all stages). */
-	struct rcu_head *nocb_follower_head; /* CBs ready to invoke. */
-	struct rcu_head **nocb_follower_tail;
-	struct swait_queue_head nocb_wq; /* For nocb kthreads to sleep on. */
-	struct task_struct *nocb_kthread;
+	struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */
+	struct task_struct *nocb_gp_kthread;
 	raw_spinlock_t nocb_lock;	/* Guard following pair of fields. */
+	atomic_t nocb_lock_contended;	/* Contention experienced. */
 	int nocb_defer_wakeup;		/* Defer wakeup of nocb_kthread. */
 	struct timer_list nocb_timer;	/* Enforce finite deferral. */
-
-	/* The following fields are used by the leader, hence own cacheline. */
-	struct rcu_head *nocb_gp_head ____cacheline_internodealigned_in_smp;
-					/* CBs waiting for GP. */
-	struct rcu_head **nocb_gp_tail;
-	bool nocb_leader_sleep;		/* Is the nocb leader thread asleep? */
-	struct rcu_data *nocb_next_follower;
-					/* Next follower in wakeup chain. */
-
-	/* The following fields are used by the follower, hence new cachline. */
-	struct rcu_data *nocb_leader ____cacheline_internodealigned_in_smp;
-					/* Leader CPU takes GP-end wakeups. */
+	unsigned long nocb_gp_adv_time;	/* Last call_rcu() CB adv (jiffies). */
+
+	/* The following fields are used by call_rcu, hence own cacheline. */
+	raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp;
+	struct rcu_cblist nocb_bypass;	/* Lock-contention-bypass CB list. */
+	unsigned long nocb_bypass_first; /* Time (jiffies) of first enqueue. */
+	unsigned long nocb_nobypass_last; /* Last ->cblist enqueue (jiffies). */
+	int nocb_nobypass_count;	/* # ->cblist enqueues at ^^^ time. */
+
+	/* The following fields are used by GP kthread, hence own cacheline. */
+	raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp;
+	struct timer_list nocb_bypass_timer; /* Force nocb_bypass flush. */
+	u8 nocb_gp_sleep;		/* Is the nocb GP thread asleep? */
+	u8 nocb_gp_bypass;		/* Found a bypass on last scan? */
+	u8 nocb_gp_gp;			/* GP to wait for on last scan? */
+	unsigned long nocb_gp_seq;	/*  If so, ->gp_seq to wait for. */
+	unsigned long nocb_gp_loops;	/* # passes through wait code. */
+	struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */
+	bool nocb_cb_sleep;		/* Is the nocb CB thread asleep? */
+	struct task_struct *nocb_cb_kthread;
+	struct rcu_data *nocb_next_cb_rdp;
+					/* Next rcu_data in wakeup chain. */
+
+	/* The following fields are used by CB kthread, hence new cacheline. */
+	struct rcu_data *nocb_gp_rdp ____cacheline_internodealigned_in_smp;
+					/* GP rdp takes GP-end wakeups. */
 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 
 	/* 6) RCU priority boosting. */
@@ -419,25 +428,39 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 static bool rcu_preempt_need_deferred_qs(struct task_struct *t);
 static void rcu_preempt_deferred_qs(struct task_struct *t);
 static void zero_cpu_stall_ticks(struct rcu_data *rdp);
-static bool rcu_nocb_cpu_needs_barrier(int cpu);
 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq);
 static void rcu_init_one_nocb(struct rcu_node *rnp);
-static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
-			    bool lazy, unsigned long flags);
-static bool rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
-				      struct rcu_data *rdp,
-				      unsigned long flags);
+static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
+				  unsigned long j);
+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 void 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);
 static void __init rcu_spawn_nocb_kthreads(void);
+static void show_rcu_nocb_state(struct rcu_data *rdp);
+static void rcu_nocb_lock(struct rcu_data *rdp);
+static void rcu_nocb_unlock(struct rcu_data *rdp);
+static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
+				       unsigned long flags);
+static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp);
 #ifdef CONFIG_RCU_NOCB_CPU
 static void __init rcu_organize_nocb_kthreads(void);
-#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
-static bool init_nocb_callback_list(struct rcu_data *rdp);
-static unsigned long rcu_get_n_cbs_nocb_cpu(struct rcu_data *rdp);
+#define rcu_nocb_lock_irqsave(rdp, flags)				\
+do {									\
+	if (!rcu_segcblist_is_offloaded(&(rdp)->cblist))		\
+		local_irq_save(flags);					\
+	else								\
+		raw_spin_lock_irqsave(&(rdp)->nocb_lock, (flags));	\
+} while (0)
+#else /* #ifdef CONFIG_RCU_NOCB_CPU */
+#define rcu_nocb_lock_irqsave(rdp, flags) local_irq_save(flags)
+#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
+
 static void rcu_bind_gp_kthread(void);
 static bool rcu_nohz_full_cpu(void);
 static void rcu_dynticks_task_enter(void);