1/* SPDX-License-Identifier: GPL-2.0-only */
  2#ifndef _KERNEL_TIME_MIGRATION_H
  3#define _KERNEL_TIME_MIGRATION_H
  4
  5/* Per group capacity. Must be a power of 2! */
  6#define TMIGR_CHILDREN_PER_GROUP 8
  7
  8/**
  9 * struct tmigr_event - a timer event associated to a CPU
 10 * @nextevt:	The node to enqueue an event in the parent group queue
 11 * @cpu:	The CPU to which this event belongs
 12 * @ignore:	Hint whether the event could be ignored; it is set when
 13 *		CPU or group is active;
 14 */
 15struct tmigr_event {
 16	struct timerqueue_node	nextevt;
 17	unsigned int		cpu;
 18	bool			ignore;
 19};
 20
 21/**
 22 * struct tmigr_group - timer migration hierarchy group
 23 * @lock:		Lock protecting the event information and group hierarchy
 24 *			information during setup
 25 * @parent:		Pointer to the parent group
 26 * @groupevt:		Next event of the group which is only used when the
 27 *			group is !active. The group event is then queued into
 28 *			the parent timer queue.
 29 *			Ignore bit of @groupevt is set when the group is active.
 30 * @next_expiry:	Base monotonic expiry time of the next event of the
 31 *			group; It is used for the racy lockless check whether a
 32 *			remote expiry is required; it is always reliable
 33 * @events:		Timer queue for child events queued in the group
 34 * @migr_state:		State of the group (see union tmigr_state)
 35 * @level:		Hierarchy level of the group; Required during setup
 36 * @numa_node:		Required for setup only to make sure CPU and low level
 37 *			group information is NUMA local. It is set to NUMA node
 38 *			as long as the group level is per NUMA node (level <
 39 *			tmigr_crossnode_level); otherwise it is set to
 40 *			NUMA_NO_NODE
 41 * @num_children:	Counter of group children to make sure the group is only
 42 *			filled with TMIGR_CHILDREN_PER_GROUP; Required for setup
 43 *			only
 44 * @childmask:		childmask of the group in the parent group; is set
 45 *			during setup and will never change; can be read
 46 *			lockless
 47 * @list:		List head that is added to the per level
 48 *			tmigr_level_list; is required during setup when a
 49 *			new group needs to be connected to the existing
 50 *			hierarchy groups
 51 */
 52struct tmigr_group {
 53	raw_spinlock_t		lock;
 54	struct tmigr_group	*parent;
 55	struct tmigr_event	groupevt;
 56	u64			next_expiry;
 57	struct timerqueue_head	events;
 58	atomic_t		migr_state;
 59	unsigned int		level;
 60	int			numa_node;
 61	unsigned int		num_children;
 62	u8			childmask;
 63	struct list_head	list;
 64};
 65
 66/**
 67 * struct tmigr_cpu - timer migration per CPU group
 68 * @lock:		Lock protecting the tmigr_cpu group information
 69 * @online:		Indicates whether the CPU is online; In deactivate path
 70 *			it is required to know whether the migrator in the top
 71 *			level group is to be set offline, while a timer is
 72 *			pending. Then another online CPU needs to be notified to
 73 *			take over the migrator role. Furthermore the information
 74 *			is required in CPU hotplug path as the CPU is able to go
 75 *			idle before the timer migration hierarchy hotplug AP is
 76 *			reached. During this phase, the CPU has to handle the
 77 *			global timers on its own and must not act as a migrator.
 78 * @idle:		Indicates whether the CPU is idle in the timer migration
 79 *			hierarchy
 80 * @remote:		Is set when timers of the CPU are expired remotely
 81 * @tmgroup:		Pointer to the parent group
 82 * @childmask:		childmask of tmigr_cpu in the parent group
 83 * @wakeup:		Stores the first timer when the timer migration
 84 *			hierarchy is completely idle and remote expiry was done;
 85 *			is returned to timer code in the idle path and is only
 86 *			used in idle path.
 87 * @cpuevt:		CPU event which could be enqueued into the parent group
 88 */
 89struct tmigr_cpu {
 90	raw_spinlock_t		lock;
 91	bool			online;
 92	bool			idle;
 93	bool			remote;
 94	struct tmigr_group	*tmgroup;
 95	u8			childmask;
 96	u64			wakeup;
 97	struct tmigr_event	cpuevt;
 98};
 99
100/**
101 * union tmigr_state - state of tmigr_group
102 * @state:	Combined version of the state - only used for atomic
103 *		read/cmpxchg function
104 * @struct:	Split version of the state - only use the struct members to
105 *		update information to stay independent of endianness
106 */
107union tmigr_state {
108	u32 state;
109	/**
110	 * struct - split state of tmigr_group
111	 * @active:	Contains each childmask bit of the active children
112	 * @migrator:	Contains childmask of the child which is migrator
113	 * @seq:	Sequence counter needs to be increased when an update
114	 *		to the tmigr_state is done. It prevents a race when
115	 *		updates in the child groups are propagated in changed
116	 *		order. Detailed information about the scenario is
117	 *		given in the documentation at the begin of
118	 *		timer_migration.c.
119	 */
120	struct {
121		u8	active;
122		u8	migrator;
123		u16	seq;
124	} __packed;
125};
126
127#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
128extern void tmigr_handle_remote(void);
129extern bool tmigr_requires_handle_remote(void);
130extern void tmigr_cpu_activate(void);
131extern u64 tmigr_cpu_deactivate(u64 nextevt);
132extern u64 tmigr_cpu_new_timer(u64 nextevt);
133extern u64 tmigr_quick_check(u64 nextevt);
134#else
135static inline void tmigr_handle_remote(void) { }
136static inline bool tmigr_requires_handle_remote(void) { return false; }
137static inline void tmigr_cpu_activate(void) { }
138#endif
139
140#endif