1 files changed, 140 insertions, 0 deletions
diff --git a/kernel/time/timer_migration.h b/kernel/time/timer_migration.h
new file mode 100644
index 000000000000..6c37d94a37d9
--- /dev/null
+++ b/kernel/time/timer_migration.h
@@ -0,0 +1,140 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _KERNEL_TIME_MIGRATION_H
+#define _KERNEL_TIME_MIGRATION_H
+
+/* Per group capacity. Must be a power of 2! */
+#define TMIGR_CHILDREN_PER_GROUP 8
+
+/**
+ * struct tmigr_event - a timer event associated to a CPU
+ * @nextevt:	The node to enqueue an event in the parent group queue
+ * @cpu:	The CPU to which this event belongs
+ * @ignore:	Hint whether the event could be ignored; it is set when
+ *		CPU or group is active;
+ */
+struct tmigr_event {
+	struct timerqueue_node	nextevt;
+	unsigned int		cpu;
+	bool			ignore;
+};
+
+/**
+ * struct tmigr_group - timer migration hierarchy group
+ * @lock:		Lock protecting the event information and group hierarchy
+ *			information during setup
+ * @parent:		Pointer to the parent group
+ * @groupevt:		Next event of the group which is only used when the
+ *			group is !active. The group event is then queued into
+ *			the parent timer queue.
+ *			Ignore bit of @groupevt is set when the group is active.
+ * @next_expiry:	Base monotonic expiry time of the next event of the
+ *			group; It is used for the racy lockless check whether a
+ *			remote expiry is required; it is always reliable
+ * @events:		Timer queue for child events queued in the group
+ * @migr_state:		State of the group (see union tmigr_state)
+ * @level:		Hierarchy level of the group; Required during setup
+ * @numa_node:		Required for setup only to make sure CPU and low level
+ *			group information is NUMA local. It is set to NUMA node
+ *			as long as the group level is per NUMA node (level <
+ *			tmigr_crossnode_level); otherwise it is set to
+ *			NUMA_NO_NODE
+ * @num_children:	Counter of group children to make sure the group is only
+ *			filled with TMIGR_CHILDREN_PER_GROUP; Required for setup
+ *			only
+ * @childmask:		childmask of the group in the parent group; is set
+ *			during setup and will never change; can be read
+ *			lockless
+ * @list:		List head that is added to the per level
+ *			tmigr_level_list; is required during setup when a
+ *			new group needs to be connected to the existing
+ *			hierarchy groups
+ */
+struct tmigr_group {
+	raw_spinlock_t		lock;
+	struct tmigr_group	*parent;
+	struct tmigr_event	groupevt;
+	u64			next_expiry;
+	struct timerqueue_head	events;
+	atomic_t		migr_state;
+	unsigned int		level;
+	int			numa_node;
+	unsigned int		num_children;
+	u8			childmask;
+	struct list_head	list;
+};
+
+/**
+ * struct tmigr_cpu - timer migration per CPU group
+ * @lock:		Lock protecting the tmigr_cpu group information
+ * @online:		Indicates whether the CPU is online; In deactivate path
+ *			it is required to know whether the migrator in the top
+ *			level group is to be set offline, while a timer is
+ *			pending. Then another online CPU needs to be notified to
+ *			take over the migrator role. Furthermore the information
+ *			is required in CPU hotplug path as the CPU is able to go
+ *			idle before the timer migration hierarchy hotplug AP is
+ *			reached. During this phase, the CPU has to handle the
+ *			global timers on its own and must not act as a migrator.
+ * @idle:		Indicates whether the CPU is idle in the timer migration
+ *			hierarchy
+ * @remote:		Is set when timers of the CPU are expired remotely
+ * @tmgroup:		Pointer to the parent group
+ * @childmask:		childmask of tmigr_cpu in the parent group
+ * @wakeup:		Stores the first timer when the timer migration
+ *			hierarchy is completely idle and remote expiry was done;
+ *			is returned to timer code in the idle path and is only
+ *			used in idle path.
+ * @cpuevt:		CPU event which could be enqueued into the parent group
+ */
+struct tmigr_cpu {
+	raw_spinlock_t		lock;
+	bool			online;
+	bool			idle;
+	bool			remote;
+	struct tmigr_group	*tmgroup;
+	u8			childmask;
+	u64			wakeup;
+	struct tmigr_event	cpuevt;
+};
+
+/**
+ * union tmigr_state - state of tmigr_group
+ * @state:	Combined version of the state - only used for atomic
+ *		read/cmpxchg function
+ * @struct:	Split version of the state - only use the struct members to
+ *		update information to stay independent of endianness
+ */
+union tmigr_state {
+	u32 state;
+	/**
+	 * struct - split state of tmigr_group
+	 * @active:	Contains each childmask bit of the active children
+	 * @migrator:	Contains childmask of the child which is migrator
+	 * @seq:	Sequence counter needs to be increased when an update
+	 *		to the tmigr_state is done. It prevents a race when
+	 *		updates in the child groups are propagated in changed
+	 *		order. Detailed information about the scenario is
+	 *		given in the documentation at the begin of
+	 *		timer_migration.c.
+	 */
+	struct {
+		u8	active;
+		u8	migrator;
+		u16	seq;
+	} __packed;
+};
+
+#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
+extern void tmigr_handle_remote(void);
+extern bool tmigr_requires_handle_remote(void);
+extern void tmigr_cpu_activate(void);
+extern u64 tmigr_cpu_deactivate(u64 nextevt);
+extern u64 tmigr_cpu_new_timer(u64 nextevt);
+extern u64 tmigr_quick_check(u64 nextevt);
+#else
+static inline void tmigr_handle_remote(void) { }
+static inline bool tmigr_requires_handle_remote(void) { return false; }
+static inline void tmigr_cpu_activate(void) { }
+#endif
+
+#endif