diff options
Diffstat (limited to 'kernel/time')
| -rw-r--r-- | kernel/time/Makefile | 3 | ||||
| -rw-r--r-- | kernel/time/tick-internal.h | 1 | ||||
| -rw-r--r-- | kernel/time/timer.c | 113 | ||||
| -rw-r--r-- | kernel/time/timer_migration.c | 1761 | ||||
| -rw-r--r-- | kernel/time/timer_migration.h | 140 |
5 files changed, 2010 insertions, 8 deletions
diff --git a/kernel/time/Makefile b/kernel/time/Makefile index 7e875e63ff3b..4af2a264a160 100644 --- a/kernel/time/Makefile +++ b/kernel/time/Makefile @@ -17,6 +17,9 @@ endif obj-$(CONFIG_GENERIC_SCHED_CLOCK) += sched_clock.o obj-$(CONFIG_TICK_ONESHOT) += tick-oneshot.o tick-sched.o obj-$(CONFIG_LEGACY_TIMER_TICK) += tick-legacy.o +ifeq ($(CONFIG_SMP),y) + obj-$(CONFIG_NO_HZ_COMMON) += timer_migration.o +endif obj-$(CONFIG_HAVE_GENERIC_VDSO) += vsyscall.o obj-$(CONFIG_DEBUG_FS) += timekeeping_debug.o obj-$(CONFIG_TEST_UDELAY) += test_udelay.o diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h index 7e3090109e33..a3243c4ac45f 100644 --- a/kernel/time/tick-internal.h +++ b/kernel/time/tick-internal.h @@ -166,6 +166,7 @@ extern void fetch_next_timer_interrupt_remote(unsigned long basej, u64 basem, extern void timer_lock_remote_bases(unsigned int cpu); extern void timer_unlock_remote_bases(unsigned int cpu); extern bool timer_base_is_idle(void); +extern void timer_expire_remote(unsigned int cpu); # endif #else /* CONFIG_NO_HZ_COMMON */ static inline void timers_update_nohz(void) { } diff --git a/kernel/time/timer.c b/kernel/time/timer.c index e02ac4607985..3ed135c8de43 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -53,6 +53,7 @@ #include <asm/io.h> #include "tick-internal.h" +#include "timer_migration.h" #define CREATE_TRACE_POINTS #include <trace/events/timer.h> @@ -2169,6 +2170,64 @@ bool timer_base_is_idle(void) { return __this_cpu_read(timer_bases[BASE_LOCAL].is_idle); } + +static void __run_timer_base(struct timer_base *base); + +/** + * timer_expire_remote() - expire global timers of cpu + * @cpu: Remote CPU + * + * Expire timers of global base of remote CPU. + */ +void timer_expire_remote(unsigned int cpu) +{ + struct timer_base *base = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu); + + __run_timer_base(base); +} + +static void timer_use_tmigr(unsigned long basej, u64 basem, + unsigned long *nextevt, bool *tick_stop_path, + bool timer_base_idle, struct timer_events *tevt) +{ + u64 next_tmigr; + + if (timer_base_idle) + next_tmigr = tmigr_cpu_new_timer(tevt->global); + else if (tick_stop_path) + next_tmigr = tmigr_cpu_deactivate(tevt->global); + else + next_tmigr = tmigr_quick_check(tevt->global); + + /* + * If the CPU is the last going idle in timer migration hierarchy, make + * sure the CPU will wake up in time to handle remote timers. + * next_tmigr == KTIME_MAX if other CPUs are still active. + */ + if (next_tmigr < tevt->local) { + u64 tmp; + + /* If we missed a tick already, force 0 delta */ + if (next_tmigr < basem) + next_tmigr = basem; + + tmp = div_u64(next_tmigr - basem, TICK_NSEC); + + *nextevt = basej + (unsigned long)tmp; + tevt->local = next_tmigr; + } +} +# else +static void timer_use_tmigr(unsigned long basej, u64 basem, + unsigned long *nextevt, bool *tick_stop_path, + bool timer_base_idle, struct timer_events *tevt) +{ + /* + * Make sure first event is written into tevt->local to not miss a + * timer on !SMP systems. + */ + tevt->local = min_t(u64, tevt->local, tevt->global); +} # endif /* CONFIG_SMP */ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem, @@ -2177,7 +2236,7 @@ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem, struct timer_events tevt = { .local = KTIME_MAX, .global = KTIME_MAX }; struct timer_base *base_local, *base_global; unsigned long nextevt; - u64 expires; + bool idle_is_possible; /* * Pretend that there is no timer pending if the cpu is offline. @@ -2199,6 +2258,22 @@ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem, base_global, &tevt); /* + * If the next event is only one jiffie ahead there is no need to call + * timer migration hierarchy related functions. The value for the next + * global timer in @tevt struct equals then KTIME_MAX. This is also + * true, when the timer base is idle. + * + * The proper timer migration hierarchy function depends on the callsite + * and whether timer base is idle or not. @nextevt will be updated when + * this CPU needs to handle the first timer migration hierarchy + * event. See timer_use_tmigr() for detailed information. + */ + idle_is_possible = time_after(nextevt, basej + 1); + if (idle_is_possible) + timer_use_tmigr(basej, basem, &nextevt, idle, + base_local->is_idle, &tevt); + + /* * We have a fresh next event. Check whether we can forward the * base. */ @@ -2210,7 +2285,10 @@ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem, */ if (idle) { /* - * Bases are idle if the next event is more than a tick away. + * Bases are idle if the next event is more than a tick + * away. Caution: @nextevt could have changed by enqueueing a + * global timer into timer migration hierarchy. Therefore a new + * check is required here. * * If the base is marked idle then any timer add operation must * forward the base clk itself to keep granularity small. This @@ -2223,14 +2301,23 @@ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem, trace_timer_base_idle(true, base_local->cpu); } *idle = base_local->is_idle; + + /* + * When timer base is not set idle, undo the effect of + * tmigr_cpu_deactivate() to prevent inconsitent states - active + * timer base but inactive timer migration hierarchy. + * + * When timer base was already marked idle, nothing will be + * changed here. + */ + if (!base_local->is_idle && idle_is_possible) + tmigr_cpu_activate(); } raw_spin_unlock(&base_global->lock); raw_spin_unlock(&base_local->lock); - expires = min_t(u64, tevt.local, tevt.global); - - return cmp_next_hrtimer_event(basem, expires); + return cmp_next_hrtimer_event(basem, tevt.local); } /** @@ -2238,8 +2325,11 @@ static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem, * @basej: base time jiffies * @basem: base time clock monotonic * - * Returns the tick aligned clock monotonic time of the next pending - * timer or KTIME_MAX if no timer is pending. + * Returns the tick aligned clock monotonic time of the next pending timer or + * KTIME_MAX if no timer is pending. If timer of global base was queued into + * timer migration hierarchy, first global timer is not taken into account. If + * it was the last CPU of timer migration hierarchy going idle, first global + * event is taken into account. */ u64 get_next_timer_interrupt(unsigned long basej, u64 basem) { @@ -2281,6 +2371,9 @@ void timer_clear_idle(void) __this_cpu_write(timer_bases[BASE_LOCAL].is_idle, false); __this_cpu_write(timer_bases[BASE_GLOBAL].is_idle, false); trace_timer_base_idle(false, smp_processor_id()); + + /* Activate without holding the timer_base->lock */ + tmigr_cpu_activate(); } #endif @@ -2350,6 +2443,9 @@ static __latent_entropy void run_timer_softirq(struct softirq_action *h) if (IS_ENABLED(CONFIG_NO_HZ_COMMON)) { run_timer_base(BASE_GLOBAL); run_timer_base(BASE_DEF); + + if (is_timers_nohz_active()) + tmigr_handle_remote(); } } @@ -2364,7 +2460,8 @@ static void run_local_timers(void) for (int i = 0; i < NR_BASES; i++, base++) { /* Raise the softirq only if required. */ - if (time_after_eq(jiffies, base->next_expiry)) { + if (time_after_eq(jiffies, base->next_expiry) || + (i == BASE_DEF && tmigr_requires_handle_remote())) { raise_softirq(TIMER_SOFTIRQ); return; } diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c new file mode 100644 index 000000000000..23cb6ea3d44e --- /dev/null +++ b/kernel/time/timer_migration.c @@ -0,0 +1,1761 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Infrastructure for migratable timers + * + * Copyright(C) 2022 linutronix GmbH + */ +#include <linux/cpuhotplug.h> +#include <linux/slab.h> +#include <linux/smp.h> +#include <linux/spinlock.h> +#include <linux/timerqueue.h> +#include <trace/events/ipi.h> + +#include "timer_migration.h" +#include "tick-internal.h" + +/* + * The timer migration mechanism is built on a hierarchy of groups. The + * lowest level group contains CPUs, the next level groups of CPU groups + * and so forth. The CPU groups are kept per node so for the normal case + * lock contention won't happen across nodes. Depending on the number of + * CPUs per node even the next level might be kept as groups of CPU groups + * per node and only the levels above cross the node topology. + * + * Example topology for a two node system with 24 CPUs each. + * + * LVL 2 [GRP2:0] + * GRP1:0 = GRP1:M + * + * LVL 1 [GRP1:0] [GRP1:1] + * GRP0:0 - GRP0:2 GRP0:3 - GRP0:5 + * + * LVL 0 [GRP0:0] [GRP0:1] [GRP0:2] [GRP0:3] [GRP0:4] [GRP0:5] + * CPUS 0-7 8-15 16-23 24-31 32-39 40-47 + * + * The groups hold a timer queue of events sorted by expiry time. These + * queues are updated when CPUs go in idle. When they come out of idle + * ignore flag of events is set. + * + * Each group has a designated migrator CPU/group as long as a CPU/group is + * active in the group. This designated role is necessary to avoid that all + * active CPUs in a group try to migrate expired timers from other CPUs, + * which would result in massive lock bouncing. + * + * When a CPU is awake, it checks in it's own timer tick the group + * hierarchy up to the point where it is assigned the migrator role or if + * no CPU is active, it also checks the groups where no migrator is set + * (TMIGR_NONE). + * + * If it finds expired timers in one of the group queues it pulls them over + * from the idle CPU and runs the timer function. After that it updates the + * group and the parent groups if required. + * + * CPUs which go idle arm their CPU local timer hardware for the next local + * (pinned) timer event. If the next migratable timer expires after the + * next local timer or the CPU has no migratable timer pending then the + * CPU does not queue an event in the LVL0 group. If the next migratable + * timer expires before the next local timer then the CPU queues that timer + * in the LVL0 group. In both cases the CPU marks itself idle in the LVL0 + * group. + * + * When CPU comes out of idle and when a group has at least a single active + * child, the ignore flag of the tmigr_event is set. This indicates, that + * the event is ignored even if it is still enqueued in the parent groups + * timer queue. It will be removed when touching the timer queue the next + * time. This spares locking in active path as the lock protects (after + * setup) only event information. For more information about locking, + * please read the section "Locking rules". + * + * If the CPU is the migrator of the group then it delegates that role to + * the next active CPU in the group or sets migrator to TMIGR_NONE when + * there is no active CPU in the group. This delegation needs to be + * propagated up the hierarchy so hand over from other leaves can happen at + * all hierarchy levels w/o doing a search. + * + * When the last CPU in the system goes idle, then it drops all migrator + * duties up to the top level of the hierarchy (LVL2 in the example). It + * then has to make sure, that it arms it's own local hardware timer for + * the earliest event in the system. + * + * + * Lifetime rules: + * --------------- + * + * The groups are built up at init time or when CPUs come online. They are + * not destroyed when a group becomes empty due to offlining. The group + * just won't participate in the hierarchy management anymore. Destroying + * groups would result in interesting race conditions which would just make + * the whole mechanism slow and complex. + * + * + * Locking rules: + * -------------- + * + * For setting up new groups and handling events it's required to lock both + * child and parent group. The lock ordering is always bottom up. This also + * includes the per CPU locks in struct tmigr_cpu. For updating the migrator and + * active CPU/group information atomic_try_cmpxchg() is used instead and only + * the per CPU tmigr_cpu->lock is held. + * + * During the setup of groups tmigr_level_list is required. It is protected by + * @tmigr_mutex. + * + * When @timer_base->lock as well as tmigr related locks are required, the lock + * ordering is: first @timer_base->lock, afterwards tmigr related locks. + * + * + * Protection of the tmigr group state information: + * ------------------------------------------------ + * + * The state information with the list of active children and migrator needs to + * be protected by a sequence counter. It prevents a race when updates in child + * groups are propagated in changed order. The state update is performed + * lockless and group wise. The following scenario describes what happens + * without updating the sequence counter: + * + * Therefore, let's take three groups and four CPUs (CPU2 and CPU3 as well + * as GRP0:1 will not change during the scenario): + * + * LVL 1 [GRP1:0] + * migrator = GRP0:1 + * active = GRP0:0, GRP0:1 + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = CPU0 migrator = CPU2 + * active = CPU0 active = CPU2 + * / \ / \ + * CPUs 0 1 2 3 + * active idle active idle + * + * + * 1. CPU0 goes idle. As the update is performed group wise, in the first step + * only GRP0:0 is updated. The update of GRP1:0 is pending as CPU0 has to + * walk the hierarchy. + * + * LVL 1 [GRP1:0] + * migrator = GRP0:1 + * active = GRP0:0, GRP0:1 + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * --> migrator = TMIGR_NONE migrator = CPU2 + * --> active = active = CPU2 + * / \ / \ + * CPUs 0 1 2 3 + * --> idle idle active idle + * + * 2. While CPU0 goes idle and continues to update the state, CPU1 comes out of + * idle. CPU1 updates GRP0:0. The update for GRP1:0 is pending as CPU1 also + * has to walk the hierarchy. Both CPUs (CPU0 and CPU1) now walk the + * hierarchy to perform the needed update from their point of view. The + * currently visible state looks the following: + * + * LVL 1 [GRP1:0] + * migrator = GRP0:1 + * active = GRP0:0, GRP0:1 + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * --> migrator = CPU1 migrator = CPU2 + * --> active = CPU1 active = CPU2 + * / \ / \ + * CPUs 0 1 2 3 + * idle --> active active idle + * + * 3. Here is the race condition: CPU1 managed to propagate its changes (from + * step 2) through the hierarchy to GRP1:0 before CPU0 (step 1) did. The + * active members of GRP1:0 remain unchanged after the update since it is + * still valid from CPU1 current point of view: + * + * LVL 1 [GRP1:0] + * --> migrator = GRP0:1 + * --> active = GRP0:0, GRP0:1 + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = CPU1 migrator = CPU2 + * active = CPU1 active = CPU2 + * / \ / \ + * CPUs 0 1 2 3 + * idle active active idle + * + * 4. Now CPU0 finally propagates its changes (from step 1) to GRP1:0. + * + * LVL 1 [GRP1:0] + * --> migrator = GRP0:1 + * --> active = GRP0:1 + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = CPU1 migrator = CPU2 + * active = CPU1 active = CPU2 + * / \ / \ + * CPUs 0 1 2 3 + * idle active active idle + * + * + * The race of CPU0 vs. CPU1 led to an inconsistent state in GRP1:0. CPU1 is + * active and is correctly listed as active in GRP0:0. However GRP1:0 does not + * have GRP0:0 listed as active, which is wrong. The sequence counter has been + * added to avoid inconsistent states during updates. The state is updated + * atomically only if all members, including the sequence counter, match the + * expected value (compare-and-exchange). + * + * Looking back at the previous example with the addition of the sequence + * counter: The update as performed by CPU0 in step 4 will fail. CPU1 changed + * the sequence number during the update in step 3 so the expected old value (as + * seen by CPU0 before starting the walk) does not match. + * + * Prevent race between new event and last CPU going inactive + * ---------------------------------------------------------- + * + * When the last CPU is going idle and there is a concurrent update of a new + * first global timer of an idle CPU, the group and child states have to be read + * while holding the lock in tmigr_update_events(). The following scenario shows + * what happens, when this is not done. + * + * 1. Only CPU2 is active: + * + * LVL 1 [GRP1:0] + * migrator = GRP0:1 + * active = GRP0:1 + * next_expiry = KTIME_MAX + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = TMIGR_NONE migrator = CPU2 + * active = active = CPU2 + * next_expiry = KTIME_MAX next_expiry = KTIME_MAX + * / \ / \ + * CPUs 0 1 2 3 + * idle idle active idle + * + * 2. Now CPU 2 goes idle (and has no global timer, that has to be handled) and + * propagates that to GRP0:1: + * + * LVL 1 [GRP1:0] + * migrator = GRP0:1 + * active = GRP0:1 + * next_expiry = KTIME_MAX + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = TMIGR_NONE --> migrator = TMIGR_NONE + * active = --> active = + * next_expiry = KTIME_MAX next_expiry = KTIME_MAX + * / \ / \ + * CPUs 0 1 2 3 + * idle idle --> idle idle + * + * 3. Now the idle state is propagated up to GRP1:0. As this is now the last + * child going idle in top level group, the expiry of the next group event + * has to be handed back to make sure no event is lost. As there is no event + * enqueued, KTIME_MAX is handed back to CPU2. + * + * LVL 1 [GRP1:0] + * --> migrator = TMIGR_NONE + * --> active = + * next_expiry = KTIME_MAX + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = TMIGR_NONE migrator = TMIGR_NONE + * active = active = + * next_expiry = KTIME_MAX next_expiry = KTIME_MAX + * / \ / \ + * CPUs 0 1 2 3 + * idle idle --> idle idle + * + * 4. CPU 0 has a new timer queued from idle and it expires at TIMER0. CPU0 + * propagates that to GRP0:0: + * + * LVL 1 [GRP1:0] + * migrator = TMIGR_NONE + * active = + * next_expiry = KTIME_MAX + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = TMIGR_NONE migrator = TMIGR_NONE + * active = active = + * --> next_expiry = TIMER0 next_expiry = KTIME_MAX + * / \ / \ + * CPUs 0 1 2 3 + * idle idle idle idle + * + * 5. GRP0:0 is not active, so the new timer has to be propagated to + * GRP1:0. Therefore the GRP1:0 state has to be read. When the stalled value + * (from step 2) is read, the timer is enqueued into GRP1:0, but nothing is + * handed back to CPU0, as it seems that there is still an active child in + * top level group. + * + * LVL 1 [GRP1:0] + * migrator = TMIGR_NONE + * active = + * --> next_expiry = TIMER0 + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = TMIGR_NONE migrator = TMIGR_NONE + * active = active = + * next_expiry = TIMER0 next_expiry = KTIME_MAX + * / \ / \ + * CPUs 0 1 2 3 + * idle idle idle idle + * + * This is prevented by reading the state when holding the lock (when a new + * timer has to be propagated from idle path):: + * + * CPU2 (tmigr_inactive_up()) CPU0 (tmigr_new_timer_up()) + * -------------------------- --------------------------- + * // step 3: + * cmpxchg(&GRP1:0->state); + * tmigr_update_events() { + * spin_lock(&GRP1:0->lock); + * // ... update events ... + * // hand back first expiry when GRP1:0 is idle + * spin_unlock(&GRP1:0->lock); + * // ^^^ release state modification + * } + * tmigr_update_events() { + * spin_lock(&GRP1:0->lock) + * // ^^^ acquire state modification + * group_state = atomic_read(&GRP1:0->state) + * // .... update events ... + * // hand back first expiry when GRP1:0 is idle + * spin_unlock(&GRP1:0->lock) <3> + * // ^^^ makes state visible for other + * // callers of tmigr_new_timer_up() + * } + * + * When CPU0 grabs the lock directly after cmpxchg, the first timer is reported + * back to CPU0 and also later on to CPU2. So no timer is missed. A concurrent + * update of the group state from active path is no problem, as the upcoming CPU + * will take care of the group events. + * + * Required event and timerqueue update after a remote expiry: + * ----------------------------------------------------------- + * + * After expiring timers of a remote CPU, a walk through the hierarchy and + * update of events and timerqueues is required. It is obviously needed if there + * is a 'new' global timer but also if there is no new global timer but the + * remote CPU is still idle. + * + * 1. CPU0 and CPU1 are idle and have both a global timer expiring at the same + * time. So both have an event enqueued in the timerqueue of GRP0:0. CPU3 is + * also idle and has no global timer pending. CPU2 is the only active CPU and + * thus also the migrator: + * + * LVL 1 [GRP1:0] + * migrator = GRP0:1 + * active = GRP0:1 + * --> timerqueue = evt-GRP0:0 + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = TMIGR_NONE migrator = CPU2 + * active = active = CPU2 + * groupevt.ignore = false groupevt.ignore = true + * groupevt.cpu = CPU0 groupevt.cpu = + * timerqueue = evt-CPU0, timerqueue = + * evt-CPU1 + * / \ / \ + * CPUs 0 1 2 3 + * idle idle active idle + * + * 2. CPU2 starts to expire remote timers. It starts with LVL0 group + * GRP0:1. There is no event queued in the timerqueue, so CPU2 continues with + * the parent of GRP0:1: GRP1:0. In GRP1:0 it dequeues the first event. It + * looks at tmigr_event::cpu struct member and expires the pending timer(s) + * of CPU0. + * + * LVL 1 [GRP1:0] + * migrator = GRP0:1 + * active = GRP0:1 + * --> timerqueue = + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = TMIGR_NONE migrator = CPU2 + * active = active = CPU2 + * groupevt.ignore = false groupevt.ignore = true + * --> groupevt.cpu = CPU0 groupevt.cpu = + * timerqueue = evt-CPU0, timerqueue = + * evt-CPU1 + * / \ / \ + * CPUs 0 1 2 3 + * idle idle active idle + * + * 3. Some work has to be done after expiring the timers of CPU0. If we stop + * here, then CPU1's pending global timer(s) will not expire in time and the + * timerqueue of GRP0:0 has still an event for CPU0 enqueued which has just + * been processed. So it is required to walk the hierarchy from CPU0's point + * of view and update it accordingly. CPU0's event will be removed from the + * timerqueue because it has no pending timer. If CPU0 would have a timer + * pending then it has to expire after CPU1's first timer because all timers + * from this period were just expired. Either way CPU1's event will be first + * in GRP0:0's timerqueue and therefore set in the CPU field of the group + * event which is then enqueued in GRP1:0's timerqueue as GRP0:0 is still not + * active: + * + * LVL 1 [GRP1:0] + * migrator = GRP0:1 + * active = GRP0:1 + * --> timerqueue = evt-GRP0:0 + * / \ + * LVL 0 [GRP0:0] [GRP0:1] + * migrator = TMIGR_NONE migrator = CPU2 + * active = active = CPU2 + * groupevt.ignore = false groupevt.ignore = true + * --> groupevt.cpu = CPU1 groupevt.cpu = + * --> timerqueue = evt-CPU1 timerqueue = + * / \ / \ + * CPUs 0 1 2 3 + * idle idle active idle + * + * Now CPU2 (migrator) will continue step 2 at GRP1:0 and will expire the + * timer(s) of CPU1. + * + * The hierarchy walk in step 3 can be skipped if the migrator notices that a + * CPU of GRP0:0 is active again. The CPU will mark GRP0:0 active and take care + * of the group as migrator and any needed updates within the hierarchy. + */ + +static DEFINE_MUTEX(tmigr_mutex); +static struct list_head *tmigr_level_list __read_mostly; + +static unsigned int tmigr_hierarchy_levels __read_mostly; +static unsigned int tmigr_crossnode_level __read_mostly; + +static DEFINE_PER_CPU(struct tmigr_cpu, tmigr_cpu); + +#define TMIGR_NONE 0xFF +#define BIT_CNT 8 + +static inline bool tmigr_is_not_available(struct tmigr_cpu *tmc) +{ + return !(tmc->tmgroup && tmc->online); +} + +/* + * Returns true, when @childmask corresponds to the group migrator or when the + * group is not active - so no migrator is set. + */ +static bool tmigr_check_migrator(struct tmigr_group *group, u8 childmask) +{ + union tmigr_state s; + + s.state = atomic_read(&group->migr_state); + + if ((s.migrator == childmask) || (s.migrator == TMIGR_NONE)) + return true; + + return false; +} + +static bool tmigr_check_migrator_and_lonely(struct tmigr_group *group, u8 childmask) +{ + bool lonely, migrator = false; + unsigned long active; + union tmigr_state s; + + s.state = atomic_read(&group->migr_state); + + if ((s.migrator == childmask) || (s.migrator == TMIGR_NONE)) + migrator = true; + + active = s.active; + lonely = bitmap_weight(&active, BIT_CNT) <= 1; + + return (migrator && lonely); +} + +static bool tmigr_check_lonely(struct tmigr_group *group) +{ + unsigned long active; + union tmigr_state s; + + s.state = atomic_read(&group->migr_state); + + active = s.active; + + return bitmap_weight(&active, BIT_CNT) <= 1; +} + +typedef bool (*up_f)(struct tmigr_group *, struct tmigr_group *, void *); + +static void __walk_groups(up_f up, void *data, + struct tmigr_cpu *tmc) +{ + struct tmigr_group *child = NULL, *group = tmc->tmgroup; + + do { + WARN_ON_ONCE(group->level >= tmigr_hierarchy_levels); + + if (up(group, child, data)) + break; + + child = group; + group = group->parent; + } while (group); +} + +static void walk_groups(up_f up, void *data, struct tmigr_cpu *tmc) +{ + lockdep_assert_held(&tmc->lock); + + __walk_groups(up, data, tmc); +} + +/** + * struct tmigr_walk - data required for walking the hierarchy + * @nextexp: Next CPU event expiry information which is handed into + * the timer migration code by the timer code + * (get_next_timer_interrupt()) + * @firstexp: Contains the first event expiry information when last + * active CPU of hierarchy is on the way to idle to make + * sure CPU will be back in time. + * @evt: Pointer to tmigr_event which needs to be queued (of idle + * child group) + * @childmask: childmask of child group + * @remote: Is set, when the new timer path is executed in + * tmigr_handle_remote_cpu() + */ +struct tmigr_walk { + u64 nextexp; + u64 firstexp; + struct tmigr_event *evt; + u8 childmask; + bool remote; +}; + +/** + * struct tmigr_remote_data - data required for remote expiry hierarchy walk + * @basej: timer base in jiffies + * @now: timer base monotonic + * @firstexp: returns expiry of the first timer in the idle timer + * migration hierarchy to make sure the timer is handled in + * time; it is stored in the per CPU tmigr_cpu struct of + * CPU which expires remote timers + * @childmask: childmask of child group + * @check: is set if there is the need to handle remote timers; + * required in tmigr_requires_handle_remote() only + * @tmc_active: this flag indicates, whether the CPU which triggers + * the hierarchy walk is !idle in the timer migration + * hierarchy. When the CPU is idle and the whole hierarchy is + * idle, only the first event of the top level has to be + * considered. + */ +struct tmigr_remote_data { + unsigned long basej; + u64 now; + u64 firstexp; + u8 childmask; + bool check; + bool tmc_active; +}; + +/* + * Returns the next event of the timerqueue @group->events + * + * Removes timers with ignore flag and update next_expiry of the group. Values + * of the group event are updated in tmigr_update_events() only. + */ +static struct tmigr_event *tmigr_next_groupevt(struct tmigr_group *group) +{ + struct timerqueue_node *node = NULL; + struct tmigr_event *evt = NULL; + + lockdep_assert_held(&group->lock); + + WRITE_ONCE(group->next_expiry, KTIME_MAX); + + while ((node = timerqueue_getnext(&group->events))) { + evt = container_of(node, struct tmigr_event, nextevt); + + if (!evt->ignore) { + WRITE_ONCE(group->next_expiry, evt->nextevt.expires); + return evt; + } + + /* + * Remove next timers with ignore flag, because the group lock + * is held anyway + */ + if (!timerqueue_del(&group->events, node)) + break; + } + + return NULL; +} + +/* + * Return the next event (with the expiry equal or before @now) + * + * Event, which is returned, is also removed from the queue. + */ +static struct tmigr_event *tmigr_next_expired_groupevt(struct tmigr_group *group, + u64 now) +{ + struct tmigr_event *evt = tmigr_next_groupevt(group); + + if (!evt || now < evt->nextevt.expires) + return NULL; + + /* + * The event is ready to expire. Remove it and update next group event. + */ + timerqueue_del(&group->events, &evt->nextevt); + tmigr_next_groupevt(group); + + return evt; +} + +static u64 tmigr_next_groupevt_expires(struct tmigr_group *group) +{ + struct tmigr_event *evt; + + evt = tmigr_next_groupevt(group); + + if (!evt) + return KTIME_MAX; + else + return evt->nextevt.expires; +} + +static bool tmigr_active_up(struct tmigr_group *group, + struct tmigr_group *child, + void *ptr) +{ + union tmigr_state curstate, newstate; + struct tmigr_walk *data = ptr; + bool walk_done; + u8 childmask; + + childmask = data->childmask; + /* + * No memory barrier is required here in contrast to + * tmigr_inactive_up(), as the group state change does not depend on the + * child state. + */ + curstate.state = atomic_read(&group->migr_state); + + do { + newstate = curstate; + walk_done = true; + + if (newstate.migrator == TMIGR_NONE) { + newstate.migrator = childmask; + + /* Changes need to be propagated */ + walk_done = false; + } + + newstate.active |= childmask; + newstate.seq++; + + } while (!atomic_try_cmpxchg(&group->migr_state, &curstate.state, newstate.state)); + + if ((walk_done == false) && group->parent) + data->childmask = group->childmask; + + /* + * The group is active (again). The group event might be still queued + * into the parent group's timerqueue but can now be handled by the + * migrator of this group. Therefore the ignore flag for the group event + * is updated to reflect this. + * + * The update of the ignore flag in the active path is done lockless. In + * worst case the migrator of the parent group observes the change too + * late and expires remotely all events belonging to this group. The + * lock is held while updating the ignore flag in idle path. So this + * state change will not be lost. + */ + group->groupevt.ignore = true; + + return walk_done; +} + +static void __tmigr_cpu_activate(struct tmigr_cpu *tmc) +{ + struct tmigr_walk data; + + data.childmask = tmc->childmask; + + tmc->cpuevt.ignore = true; + WRITE_ONCE(tmc->wakeup, KTIME_MAX); + + walk_groups(&tmigr_active_up, &data, tmc); +} + +/** + * tmigr_cpu_activate() - set this CPU active in timer migration hierarchy + * + * Call site timer_clear_idle() is called with interrupts disabled. + */ +void tmigr_cpu_activate(void) +{ + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); + + if (tmigr_is_not_available(tmc)) + return; + + if (WARN_ON_ONCE(!tmc->idle)) + return; + + raw_spin_lock(&tmc->lock); + tmc->idle = false; + __tmigr_cpu_activate(tmc); + raw_spin_unlock(&tmc->lock); +} + +/* + * Returns true, if there is nothing to be propagated to the next level + * + * @data->firstexp is set to expiry of first gobal event of the (top level of + * the) hierarchy, but only when hierarchy is completely idle. + * + * The child and group states need to be read under the lock, to prevent a race + * against a concurrent tmigr_inactive_up() run when the last CPU goes idle. See + * also section "Prevent race between new event and last CPU going inactive" in + * the documentation at the top. + * + * This is the only place where the group event expiry value is set. + */ +static +bool tmigr_update_events(struct tmigr_group *group, struct tmigr_group *child, + struct tmigr_walk *data) +{ + struct tmigr_event *evt, *first_childevt; + union tmigr_state childstate, groupstate; + bool remote = data->remote; + bool walk_done = false; + u64 nextexp; + + if (child) { + raw_spin_lock(&child->lock); + raw_spin_lock_nested(&group->lock, SINGLE_DEPTH_NESTING); + + childstate.state = atomic_read(&child->migr_state); + groupstate.state = atomic_read(&group->migr_state); + + if (childstate.active) { + walk_done = true; + goto unlock; + } + + first_childevt = tmigr_next_groupevt(child); + nextexp = child->next_expiry; + evt = &child->groupevt; + + evt->ignore = (nextexp == KTIME_MAX) ? true : false; + } else { + nextexp = data->nextexp; + + first_childevt = evt = data->evt; + + /* + * Walking the hierarchy is required in any case when a + * remote expiry was done before. This ensures to not lose + * already queued events in non active groups (see section + * "Required event and timerqueue update after a remote + * expiry" in the documentation at the top). + * + * The two call sites which are executed without a remote expiry + * before, are not prevented from propagating changes through + * the hierarchy by the return: + * - When entering this path by tmigr_new_timer(), @evt->ignore + * is never set. + * - tmigr_inactive_up() takes care of the propagation by + * itself and ignores the return value. But an immediate + * return is required because nothing has to be done in this + * level as the event could be ignored. + */ + if (evt->ignore && !remote) + return true; + + raw_spin_lock(&group->lock); + + childstate.state = 0; + groupstate.state = atomic_read(&group->migr_state); + } + + /* + * If the child event is already queued in the group, remove it from the + * queue when the expiry time changed only or when it could be ignored. + */ + if (timerqueue_node_queued(&evt->nextevt)) { + if ((evt->nextevt.expires == nextexp) && !evt->ignore) + goto check_toplvl; + + if (!timerqueue_del(&group->events, &evt->nextevt)) + WRITE_ONCE(group->next_expiry, KTIME_MAX); + } + + if (evt->ignore) { + /* + * When the next child event could be ignored (nextexp is + * KTIME_MAX) and there was no remote timer handling before or + * the group is already active, there is no need to walk the + * hierarchy even if there is a parent group. + * + * The other way round: even if the event could be ignored, but + * if a remote timer handling was executed before and the group + * is not active, walking the hierarchy is required to not miss + * an enqueued timer in the non active group. The enqueued timer + * of the group needs to be propagated to a higher level to + * ensure it is handled. + */ + if (!remote || groupstate.active) + walk_done = true; + } else { + evt->nextevt.expires = nextexp; + evt->cpu = first_childevt->cpu; + + if (timerqueue_add(&group->events, &evt->nextevt)) + WRITE_ONCE(group->next_expiry, nextexp); + } + +check_toplvl: + if (!group->parent && (groupstate.migrator == TMIGR_NONE)) { + walk_done = true; + + /* + * Nothing to do when update was done during remote timer + * handling. First timer in top level group which needs to be + * handled when top level group is not active, is calculated + * directly in tmigr_handle_remote_up(). + */ + if (remote) + goto unlock; + + /* + * The top level group is idle and it has to be ensured the + * global timers are handled in time. (This could be optimized + * by keeping track of the last global scheduled event and only + * arming it on the CPU if the new event is earlier. Not sure if + * its worth the complexity.) + */ + data->firstexp = tmigr_next_groupevt_expires(group); + } + +unlock: + raw_spin_unlock(&group->lock); + + if (child) + raw_spin_unlock(&child->lock); + + return walk_done; +} + +static bool tmigr_new_timer_up(struct tmigr_group *group, + struct tmigr_group *child, + void *ptr) +{ + struct tmigr_walk *data = ptr; + + return tmigr_update_events(group, child, data); +} + +/* + * Returns the expiry of the next timer that needs to be handled. KTIME_MAX is + * returned, if an active CPU will handle all the timer migration hierarchy + * timers. + */ +static u64 tmigr_new_timer(struct tmigr_cpu *tmc, u64 nextexp) +{ + struct tmigr_walk data = { .nextexp = nextexp, + .firstexp = KTIME_MAX, + .evt = &tmc->cpuevt }; + + lockdep_assert_held(&tmc->lock); + + if (tmc->remote) + return KTIME_MAX; + + tmc->cpuevt.ignore = false; + data.remote = false; + + walk_groups(&tmigr_new_timer_up, &data, tmc); + + /* If there is a new first global event, make sure it is handled */ + return data.firstexp; +} + +static void tmigr_handle_remote_cpu(unsigned int cpu, u64 now, + unsigned long jif) +{ + struct timer_events tevt; + struct tmigr_walk data; + struct tmigr_cpu *tmc; + + tmc = per_cpu_ptr(&tmigr_cpu, cpu); + + raw_spin_lock_irq(&tmc->lock); + + /* + * If the remote CPU is offline then the timers have been migrated to + * another CPU. + * + * If tmigr_cpu::remote is set, at the moment another CPU already + * expires the timers of the remote CPU. + * + * If tmigr_event::ignore is set, then the CPU returns from idle and + * takes care of its timers. + * + * If the next event expires in the future, then the event has been + * updated and there are no timers to expire right now. The CPU which + * updated the event takes care when hierarchy is completely + * idle. Otherwise the migrator does it as the event is enqueued. + */ + if (!tmc->online || tmc->remote || tmc->cpuevt.ignore || + now < tmc->cpuevt.nextevt.expires) { + raw_spin_unlock_irq(&tmc->lock); + return; + } + + tmc->remote = true; + WRITE_ONCE(tmc->wakeup, KTIME_MAX); + + /* Drop the lock to allow the remote CPU to exit idle */ + raw_spin_unlock_irq(&tmc->lock); + + if (cpu != smp_processor_id()) + timer_expire_remote(cpu); + + /* + * Lock ordering needs to be preserved - timer_base locks before tmigr + * related locks (see section "Locking rules" in the documentation at + * the top). During fetching the next timer interrupt, also tmc->lock + * needs to be held. Otherwise there is a possible race window against + * the CPU itself when it comes out of idle, updates the first timer in + * the hierarchy and goes back to idle. + * + * timer base locks are dropped as fast as possible: After checking + * whether the remote CPU went offline in the meantime and after + * fetching the next remote timer interrupt. Dropping the locks as fast + * as possible keeps the locking region small and prevents holding + * several (unnecessary) locks during walking the hierarchy for updating + * the timerqueue and group events. + */ + local_irq_disable(); + timer_lock_remote_bases(cpu); + raw_spin_lock(&tmc->lock); + + /* + * When the CPU went offline in the meantime, no hierarchy walk has to + * be done for updating the queued events, because the walk was + * already done during marking the CPU offline in the hierarchy. + * + * When the CPU is no longer idle, the CPU takes care of the timers and + * also of the timers in the hierarchy. + * + * (See also section "Required event and timerqueue update after a + * remote expiry" in the documentation at the top) + */ + if (!tmc->online || !tmc->idle) { + timer_unlock_remote_bases(cpu); + goto unlock; + } + + /* next event of CPU */ + fetch_next_timer_interrupt_remote(jif, now, &tevt, cpu); + timer_unlock_remote_bases(cpu); + + data.nextexp = tevt.global; + data.firstexp = KTIME_MAX; + data.evt = &tmc->cpuevt; + data.remote = true; + + /* + * The update is done even when there is no 'new' global timer pending + * on the remote CPU (see section "Required event and timerqueue update + * after a remote expiry" in the documentation at the top) + */ + walk_groups(&tmigr_new_timer_up, &data, tmc); + +unlock: + tmc->remote = false; + raw_spin_unlock_irq(&tmc->lock); +} + +static bool tmigr_handle_remote_up(struct tmigr_group *group, + struct tmigr_group *child, + void *ptr) +{ + struct tmigr_remote_data *data = ptr; + struct tmigr_event *evt; + unsigned long jif; + u8 childmask; + u64 now; + + jif = data->basej; + now = data->now; + + childmask = data->childmask; + +again: + /* + * Handle the group only if @childmask is the migrator or if the + * group has no migrator. Otherwise the group is active and is + * handled by its own migrator. + */ + if (!tmigr_check_migrator(group, childmask)) + return true; + + raw_spin_lock_irq(&group->lock); + + evt = tmigr_next_expired_groupevt(group, now); + + if (evt) { + unsigned int remote_cpu = evt->cpu; + + raw_spin_unlock_irq(&group->lock); + + tmigr_handle_remote_cpu(remote_cpu, now, jif); + + /* check if there is another event, that needs to be handled */ + goto again; + } + + /* + * Update of childmask for the next level and keep track of the expiry + * of the first event that needs to be handled (group->next_expiry was + * updated by tmigr_next_expired_groupevt(), next was set by + * tmigr_handle_remote_cpu()). + */ + data->childmask = group->childmask; + data->firstexp = group->next_expiry; + + raw_spin_unlock_irq(&group->lock); + + return false; +} + +/** + * tmigr_handle_remote() - Handle global timers of remote idle CPUs + * + * Called from the timer soft interrupt with interrupts enabled. + */ +void tmigr_handle_remote(void) +{ + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); + struct tmigr_remote_data data; + + if (tmigr_is_not_available(tmc)) + return; + + data.childmask = tmc->childmask; + data.firstexp = KTIME_MAX; + + /* + * NOTE: This is a doubled check because the migrator test will be done + * in tmigr_handle_remote_up() anyway. Keep this check to speed up the + * return when nothing has to be done. + */ + if (!tmigr_check_migrator(tmc->tmgroup, tmc->childmask)) + return; + + data.now = get_jiffies_update(&data.basej); + + /* + * Update @tmc->wakeup only at the end and do not reset @tmc->wakeup to + * KTIME_MAX. Even if tmc->lock is not held during the whole remote + * handling, tmc->wakeup is fine to be stale as it is called in + * interrupt context and tick_nohz_next_event() is executed in interrupt + * exit path only after processing the last pending interrupt. + */ + + __walk_groups(&tmigr_handle_remote_up, &data, tmc); + + raw_spin_lock_irq(&tmc->lock); + WRITE_ONCE(tmc->wakeup, data.firstexp); + raw_spin_unlock_irq(&tmc->lock); +} + +static bool tmigr_requires_handle_remote_up(struct tmigr_group *group, + struct tmigr_group *child, + void *ptr) +{ + struct tmigr_remote_data *data = ptr; + u8 childmask; + + childmask = data->childmask; + + /* + * Handle the group only if the child is the migrator or if the group + * has no migrator. Otherwise the group is active and is handled by its + * own migrator. + */ + if (!tmigr_check_migrator(group, childmask)) + return true; + + /* + * When there is a parent group and the CPU which triggered the + * hierarchy walk is not active, proceed the walk to reach the top level + * group before reading the next_expiry value. + */ + if (group->parent && !data->tmc_active) + goto out; + + /* + * The lock is required on 32bit architectures to read the variable + * consistently with a concurrent writer. On 64bit the lock is not + * required because the read operation is not split and so it is always + * consistent. + */ + if (IS_ENABLED(CONFIG_64BIT)) { + data->firstexp = READ_ONCE(group->next_expiry); + if (data->now >= data->firstexp) { + data->check = true; + return true; + } + } else { + raw_spin_lock(&group->lock); + data->firstexp = group->next_expiry; + if (data->now >= group->next_expiry) { + data->check = true; + raw_spin_unlock(&group->lock); + return true; + } + raw_spin_unlock(&group->lock); + } + +out: + /* Update of childmask for the next level */ + data->childmask = group->childmask; + return false; +} + +/** + * tmigr_requires_handle_remote() - Check the need of remote timer handling + * + * Must be called with interrupts disabled. + */ +bool tmigr_requires_handle_remote(void) +{ + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); + struct tmigr_remote_data data; + unsigned long jif; + bool ret = false; + + if (tmigr_is_not_available(tmc)) + return ret; + + data.now = get_jiffies_update(&jif); + data.childmask = tmc->childmask; + data.firstexp = KTIME_MAX; + data.tmc_active = !tmc->idle; + data.check = false; + + /* + * If the CPU is active, walk the hierarchy to check whether a remote + * expiry is required. + * + * Check is done lockless as interrupts are disabled and @tmc->idle is + * set only by the local CPU. + */ + if (!tmc->idle) { + __walk_groups(&tmigr_requires_handle_remote_up, &data, tmc); + + return data.check; + } + + /* + * When the CPU is idle, compare @tmc->wakeup with @data.now. The lock + * is required on 32bit architectures to read the variable consistently + * with a concurrent writer. On 64bit the lock is not required because + * the read operation is not split and so it is always consistent. + */ + if (IS_ENABLED(CONFIG_64BIT)) { + if (data.now >= READ_ONCE(tmc->wakeup)) + return true; + } else { + raw_spin_lock(&tmc->lock); + if (data.now >= tmc->wakeup) + ret = true; + raw_spin_unlock(&tmc->lock); + } + + return ret; +} + +/** + * tmigr_cpu_new_timer() - enqueue next global timer into hierarchy (idle tmc) + * @nextexp: Next expiry of global timer (or KTIME_MAX if not) + * + * The CPU is already deactivated in the timer migration + * hierarchy. tick_nohz_get_sleep_length() calls tick_nohz_next_event() + * and thereby the timer idle path is executed once more. @tmc->wakeup + * holds the first timer, when the timer migration hierarchy is + * completely idle. + * + * Returns the first timer that needs to be handled by this CPU or KTIME_MAX if + * nothing needs to be done. + */ +u64 tmigr_cpu_new_timer(u64 nextexp) +{ + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); + u64 ret; + + if (tmigr_is_not_available(tmc)) + return nextexp; + + raw_spin_lock(&tmc->lock); + + ret = READ_ONCE(tmc->wakeup); + if (nextexp != KTIME_MAX) { + if (nextexp != tmc->cpuevt.nextevt.expires || + tmc->cpuevt.ignore) { + ret = tmigr_new_timer(tmc, nextexp); + } + } + /* + * Make sure the reevaluation of timers in idle path will not miss an + * event. + */ + WRITE_ONCE(tmc->wakeup, ret); + + raw_spin_unlock(&tmc->lock); + return ret; +} + +static bool tmigr_inactive_up(struct tmigr_group *group, + struct tmigr_group *child, + void *ptr) +{ + union tmigr_state curstate, newstate, childstate; + struct tmigr_walk *data = ptr; + bool walk_done; + u8 childmask; + + childmask = data->childmask; + childstate.state = 0; + + /* + * The memory barrier is paired with the cmpxchg() in tmigr_active_up() + * to make sure the updates of child and group states are ordered. The + * ordering is mandatory, as the group state change depends on the child + * state. + */ + curstate.state = atomic_read_acquire(&group->migr_state); + + for (;;) { + if (child) + childstate.state = atomic_read(&child->migr_state); + + newstate = curstate; + walk_done = true; + + /* Reset active bit when the child is no longer active */ + if (!childstate.active) + newstate.active &= ~childmask; + + if (newstate.migrator == childmask) { + /* + * Find a new migrator for the group, because the child + * group is idle! + */ + if (!childstate.active) { + unsigned long new_migr_bit, active = newstate.active; + + new_migr_bit = find_first_bit(&active, BIT_CNT); + + if (new_migr_bit != BIT_CNT) { + newstate.migrator = BIT(new_migr_bit); + } else { + newstate.migrator = TMIGR_NONE; + + /* Changes need to be propagated */ + walk_done = false; + } + } + } + + newstate.seq++; + + WARN_ON_ONCE((newstate.migrator != TMIGR_NONE) && !(newstate.active)); + + if (atomic_try_cmpxchg(&group->migr_state, &curstate.state, + newstate.state)) + break; + + /* + * The memory barrier is paired with the cmpxchg() in + * tmigr_active_up() to make sure the updates of child and group + * states are ordered. It is required only when the above + * try_cmpxchg() fails. + */ + smp_mb__after_atomic(); + } + + data->remote = false; + + /* Event Handling */ + tmigr_update_events(group, child, data); + + if (group->parent && (walk_done == false)) + data->childmask = group->childmask; + + /* + * data->firstexp was set by tmigr_update_events() and contains the + * expiry of the first global event which needs to be handled. It + * differs from KTIME_MAX if: + * - group is the top level group and + * - group is idle (which means CPU was the last active CPU in the + * hierarchy) and + * - there is a pending event in the hierarchy + */ + WARN_ON_ONCE(data->firstexp != KTIME_MAX && group->parent); + + return walk_done; +} + +static u64 __tmigr_cpu_deactivate(struct tmigr_cpu *tmc, u64 nextexp) +{ + struct tmigr_walk data = { .nextexp = nextexp, + .firstexp = KTIME_MAX, + .evt = &tmc->cpuevt, + .childmask = tmc->childmask }; + + /* + * If nextexp is KTIME_MAX, the CPU event will be ignored because the + * local timer expires before the global timer, no global timer is set + * or CPU goes offline. + */ + if (nextexp != KTIME_MAX) + tmc->cpuevt.ignore = false; + + walk_groups(&tmigr_inactive_up, &data, tmc); + return data.firstexp; +} + +/** + * tmigr_cpu_deactivate() - Put current CPU into inactive state + * @nextexp: The next global timer expiry of the current CPU + * + * Must be called with interrupts disabled. + * + * Return: the next event expiry of the current CPU or the next event expiry + * from the hierarchy if this CPU is the top level migrator or the hierarchy is + * completely idle. + */ +u64 tmigr_cpu_deactivate(u64 nextexp) +{ + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); + u64 ret; + + if (tmigr_is_not_available(tmc)) + return nextexp; + + raw_spin_lock(&tmc->lock); + + ret = __tmigr_cpu_deactivate(tmc, nextexp); + + tmc->idle = true; + + /* + * Make sure the reevaluation of timers in idle path will not miss an + * event. + */ + WRITE_ONCE(tmc->wakeup, ret); + + raw_spin_unlock(&tmc->lock); + return ret; +} + +/** + * tmigr_quick_check() - Quick forecast of next tmigr event when CPU wants to + * go idle + * @nextevt: The next global timer expiry of the current CPU + * + * Return: + * * KTIME_MAX - when it is probable that nothing has to be done (not + * the only one in the level 0 group; and if it is the + * only one in level 0 group, but there are more than a + * single group active on the way to top level) + * * nextevt - when CPU is offline and has to handle timer on his own + * or when on the way to top in every group only a single + * child is active and but @nextevt is before next_expiry + * of top level group + * * next_expiry (top) - value of top level group, when on the way to top in + * every group only a single child is active and @nextevt + * is after this value active child. + */ +u64 tmigr_quick_check(u64 nextevt) +{ + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); + struct tmigr_group *group = tmc->tmgroup; + + if (tmigr_is_not_available(tmc)) + return nextevt; + + if (WARN_ON_ONCE(tmc->idle)) + return nextevt; + + if (!tmigr_check_migrator_and_lonely(tmc->tmgroup, tmc->childmask)) + return KTIME_MAX; + + do { + if (!tmigr_check_lonely(group)) { + return KTIME_MAX; + } else if (!group->parent) { + u64 first_global = READ_ONCE(group->next_expiry); + + return min_t(u64, nextevt, first_global); + } + group = group->parent; + } while (group); + + return KTIME_MAX; +} + +static void tmigr_init_group(struct tmigr_group *group, unsigned int lvl, + int node) +{ + union tmigr_state s; + + raw_spin_lock_init(&group->lock); + + group->level = lvl; + group->numa_node = lvl < tmigr_crossnode_level ? node : NUMA_NO_NODE; + + group->num_children = 0; + + s.migrator = TMIGR_NONE; + s.active = 0; + s.seq = 0; + atomic_set(&group->migr_state, s.state); + + timerqueue_init_head(&group->events); + timerqueue_init(&group->groupevt.nextevt); + group->groupevt.nextevt.expires = KTIME_MAX; + WRITE_ONCE(group->next_expiry, KTIME_MAX); + group->groupevt.ignore = true; +} + +static struct tmigr_group *tmigr_get_group(unsigned int cpu, int node, + unsigned int lvl) +{ + struct tmigr_group *tmp, *group = NULL; + + lockdep_assert_held(&tmigr_mutex); + + /* Try to attach to an existing group first */ + list_for_each_entry(tmp, &tmigr_level_list[lvl], list) { + /* + * If @lvl is below the cross NUMA node level, check whether + * this group belongs to the same NUMA node. + */ + if (lvl < tmigr_crossnode_level && tmp->numa_node != node) + continue; + + /* Capacity left? */ + if (tmp->num_children >= TMIGR_CHILDREN_PER_GROUP) + continue; + + /* + * TODO: A possible further improvement: Make sure that all CPU + * siblings end up in the same group of the lowest level of the + * hierarchy. Rely on the topology sibling mask would be a + * reasonable solution. + */ + + group = tmp; + break; + } + + if (group) + return group; + + /* Allocate and set up a new group */ + group = kzalloc_node(sizeof(*group), GFP_KERNEL, node); + if (!group) + return ERR_PTR(-ENOMEM); + + tmigr_init_group(group, lvl, node); + + /* Setup successful. Add it to the hierarchy */ + list_add(&group->list, &tmigr_level_list[lvl]); + return group; +} + +static void tmigr_connect_child_parent(struct tmigr_group *child, + struct tmigr_group *parent) +{ + union tmigr_state childstate; + + raw_spin_lock_irq(&child->lock); + raw_spin_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING); + + child->parent = parent; + child->childmask = BIT(parent->num_children++); + + raw_spin_unlock(&parent->lock); + raw_spin_unlock_irq(&child->lock); + + /* + * To prevent inconsistent states, active children need to be active in + * the new parent as well. Inactive children are already marked inactive + * in the parent group: + * + * * When new groups were created by tmigr_setup_groups() starting from + * the lowest level (and not higher then one level below the current + * top level), then they are not active. They will be set active when + * the new online CPU comes active. + * + * * But if a new group above the current top level is required, it is + * mandatory to propagate the active state of the already existing + * child to the new parent. So tmigr_connect_child_parent() is + * executed with the formerly top level group (child) and the newly + * created group (parent). + */ + childstate.state = atomic_read(&child->migr_state); + if (childstate.migrator != TMIGR_NONE) { + struct tmigr_walk data; + + data.childmask = child->childmask; + + /* + * There is only one new level per time. When connecting the + * child and the parent and set the child active when the parent + * is inactive, the parent needs to be the uppermost + * level. Otherwise there went something wrong! + */ + WARN_ON(!tmigr_active_up(parent, child, &data) && parent->parent); + } +} + +static int tmigr_setup_groups(unsigned int cpu, unsigned int node) +{ + struct tmigr_group *group, *child, **stack; + int top = 0, err = 0, i = 0; + struct list_head *lvllist; + + stack = kcalloc(tmigr_hierarchy_levels, sizeof(*stack), GFP_KERNEL); + if (!stack) + return -ENOMEM; + + do { + group = tmigr_get_group(cpu, node, i); + if (IS_ERR(group)) { + err = PTR_ERR(group); + break; + } + + top = i; + stack[i++] = group; + + /* + * When booting only less CPUs of a system than CPUs are + * available, not all calculated hierarchy levels are required. + * + * The loop is aborted as soon as the highest level, which might + * be different from tmigr_hierarchy_levels, contains only a + * single group. + */ + if (group->parent || i == tmigr_hierarchy_levels || + (list_empty(&tmigr_level_list[i]) && + list_is_singular(&tmigr_level_list[i - 1]))) + break; + + } while (i < tmigr_hierarchy_levels); + + do { + group = stack[--i]; + + if (err < 0) { + list_del(&group->list); + kfree(group); + continue; + } + + WARN_ON_ONCE(i != group->level); + + /* + * Update tmc -> group / child -> group connection + */ + if (i == 0) { + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); + + raw_spin_lock_irq(&group->lock); + + tmc->tmgroup = group; + tmc->childmask = BIT(group->num_children++); + + raw_spin_unlock_irq(&group->lock); + + /* There are no children that need to be connected */ + continue; + } else { + child = stack[i - 1]; + tmigr_connect_child_parent(child, group); + } + + /* check if uppermost level was newly created */ + if (top != i) + continue; + + WARN_ON_ONCE(top == 0); + + lvllist = &tmigr_level_list[top]; + if (group->num_children == 1 && list_is_singular(lvllist)) { + lvllist = &tmigr_level_list[top - 1]; + list_for_each_entry(child, lvllist, list) { + if (child->parent) + continue; + + tmigr_connect_child_parent(child, group); + } + } + } while (i > 0); + + kfree(stack); + + return err; +} + +static int tmigr_add_cpu(unsigned int cpu) +{ + int node = cpu_to_node(cpu); + int ret; + + mutex_lock(&tmigr_mutex); + ret = tmigr_setup_groups(cpu, node); + mutex_unlock(&tmigr_mutex); + + return ret; +} + +static int tmigr_cpu_online(unsigned int cpu) +{ + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); + int ret; + + /* First online attempt? Initialize CPU data */ + if (!tmc->tmgroup) { + raw_spin_lock_init(&tmc->lock); + + ret = tmigr_add_cpu(cpu); + if (ret < 0) + return ret; + + if (tmc->childmask == 0) + return -EINVAL; + + timerqueue_init(&tmc->cpuevt.nextevt); + tmc->cpuevt.nextevt.expires = KTIME_MAX; + tmc->cpuevt.ignore = true; + tmc->cpuevt.cpu = cpu; + + tmc->remote = false; + WRITE_ONCE(tmc->wakeup, KTIME_MAX); + } + raw_spin_lock_irq(&tmc->lock); + tmc->idle = timer_base_is_idle(); + if (!tmc->idle) + __tmigr_cpu_activate(tmc); + tmc->online = true; + raw_spin_unlock_irq(&tmc->lock); + return 0; +} + +/* + * tmigr_trigger_active() - trigger a CPU to become active again + * + * This function is executed on a CPU which is part of cpu_online_mask, when the + * last active CPU in the hierarchy is offlining. With this, it is ensured that + * the other CPU is active and takes over the migrator duty. + */ +static long tmigr_trigger_active(void *unused) +{ + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); + + WARN_ON_ONCE(!tmc->online || tmc->idle); + + return 0; +} + +static int tmigr_cpu_offline(unsigned int cpu) +{ + struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu); + int migrator; + u64 firstexp; + + raw_spin_lock_irq(&tmc->lock); + tmc->online = false; + WRITE_ONCE(tmc->wakeup, KTIME_MAX); + + /* + * CPU has to handle the local events on his own, when on the way to + * offline; Therefore nextevt value is set to KTIME_MAX + */ + firstexp = __tmigr_cpu_deactivate(tmc, KTIME_MAX); + raw_spin_unlock_irq(&tmc->lock); + + if (firstexp != KTIME_MAX) { + migrator = cpumask_any_but(cpu_online_mask, cpu); + work_on_cpu(migrator, tmigr_trigger_active, NULL); + } + + return 0; +} + +static int __init tmigr_init(void) +{ + unsigned int cpulvl, nodelvl, cpus_per_node, i; + unsigned int nnodes = num_possible_nodes(); + unsigned int ncpus = num_possible_cpus(); + int ret = -ENOMEM; + + BUILD_BUG_ON_NOT_POWER_OF_2(TMIGR_CHILDREN_PER_GROUP); + + /* Nothing to do if running on UP */ + if (ncpus == 1) + return 0; + + /* + * Calculate the required hierarchy levels. Unfortunately there is no + * reliable information available, unless all possible CPUs have been + * brought up and all NUMA nodes are populated. + * + * Estimate the number of levels with the number of possible nodes and + * the number of possible CPUs. Assume CPUs are spread evenly across + * nodes. We cannot rely on cpumask_of_node() because it only works for + * online CPUs. + */ + cpus_per_node = DIV_ROUND_UP(ncpus, nnodes); + + /* Calc the hierarchy levels required to hold the CPUs of a node */ + cpulvl = DIV_ROUND_UP(order_base_2(cpus_per_node), + ilog2(TMIGR_CHILDREN_PER_GROUP)); + + /* Calculate the extra levels to connect all nodes */ + nodelvl = DIV_ROUND_UP(order_base_2(nnodes), + ilog2(TMIGR_CHILDREN_PER_GROUP)); + + tmigr_hierarchy_levels = cpulvl + nodelvl; + + /* + * If a NUMA node spawns more than one CPU level group then the next + * level(s) of the hierarchy contains groups which handle all CPU groups + * of the same NUMA node. The level above goes across NUMA nodes. Store + * this information for the setup code to decide in which level node + * matching is no longer required. + */ + tmigr_crossnode_level = cpulvl; + + tmigr_level_list = kcalloc(tmigr_hierarchy_levels, sizeof(struct list_head), GFP_KERNEL); + if (!tmigr_level_list) + goto err; + + for (i = 0; i < tmigr_hierarchy_levels; i++) + INIT_LIST_HEAD(&tmigr_level_list[i]); + + pr_info("Timer migration: %d hierarchy levels; %d children per group;" + " %d crossnode level\n", + tmigr_hierarchy_levels, TMIGR_CHILDREN_PER_GROUP, + tmigr_crossnode_level); + + ret = cpuhp_setup_state(CPUHP_AP_TMIGR_ONLINE, "tmigr:online", + tmigr_cpu_online, tmigr_cpu_offline); + if (ret) + goto err; + + return 0; + +err: + pr_err("Timer migration setup failed\n"); + return ret; +} +late_initcall(tmigr_init); 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 |