Context: Full dynticks (NOHZ_FULL) is typically a static configuration determined at boot time. DHEI extends this to support runtime activation.
Problem: Switching to NOHZ_FULL at runtime requires careful synchronization of context tracking and housekeeping states. Re-invoking setup logic multiple times could lead to inconsistencies or warnings, and RCU dependency checks often prevented tick suppression in Zero-Conf setups. Solution: - Replace the static tick_nohz_full_enabled() checks with a dynamic tick_nohz_full_running state variable. - Refactor tick_nohz_full_setup to be safe for runtime invocation, adding guards against re-initialization and ensuring IRQ work interrupt support. - Implement boot-time pre-activation of context tracking (shadow init) for all possible CPUs to avoid instruction flow issues during dynamic transitions. - Hook into housekeeping_notifier_list to update NO_HZ states dynamically. This provides the core state machine for reliable, on-demand tick suppression and high-performance isolation. Signed-off-by: Qiliang Yuan <[email protected]> --- kernel/time/tick-sched.c | 130 ++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 105 insertions(+), 25 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index f7907fadd63f2..23d69d7d44538 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -27,6 +27,7 @@ #include <linux/posix-timers.h> #include <linux/context_tracking.h> #include <linux/mm.h> +#include <linux/sched/isolation.h> #include <asm/irq_regs.h> @@ -624,13 +625,25 @@ void __tick_nohz_task_switch(void) /* Get the boot-time nohz CPU list from the kernel parameters. */ void __init tick_nohz_full_setup(cpumask_var_t cpumask) { - alloc_bootmem_cpumask_var(&tick_nohz_full_mask); + if (!tick_nohz_full_mask) { + if (!slab_is_available()) + alloc_bootmem_cpumask_var(&tick_nohz_full_mask); + else + zalloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL); + } cpumask_copy(tick_nohz_full_mask, cpumask); tick_nohz_full_running = true; } bool tick_nohz_cpu_hotpluggable(unsigned int cpu) { + /* + * Allow all CPUs to go down during shutdown/reboot to avoid + * interfering with the final power-off sequence. + */ + if (system_state > SYSTEM_RUNNING) + return true; + /* * The 'tick_do_timer_cpu' CPU handles housekeeping duty (unbound * timers, workqueues, timekeeping, ...) on behalf of full dynticks @@ -646,45 +659,112 @@ static int tick_nohz_cpu_down(unsigned int cpu) return tick_nohz_cpu_hotpluggable(cpu) ? 0 : -EBUSY; } +static int tick_nohz_housekeeping_reconfigure(struct notifier_block *nb, + unsigned long action, void *data) +{ + struct housekeeping_update *upd = data; + int cpu; + + if (action == HK_UPDATE_MASK && upd->type == HK_TYPE_TICK) { + cpumask_var_t non_housekeeping_mask; + + if (!alloc_cpumask_var(&non_housekeeping_mask, GFP_KERNEL)) + return NOTIFY_BAD; + + cpumask_andnot(non_housekeeping_mask, cpu_possible_mask, upd->new_mask); + + if (!tick_nohz_full_mask) { + if (!zalloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) { + free_cpumask_var(non_housekeeping_mask); + return NOTIFY_BAD; + } + } + + /* Kick all CPUs to re-evaluate tick dependency before change */ + for_each_online_cpu(cpu) + tick_nohz_full_kick_cpu(cpu); + + cpumask_copy(tick_nohz_full_mask, non_housekeeping_mask); + tick_nohz_full_running = !cpumask_empty(tick_nohz_full_mask); + + /* + * If nohz_full is running, the timer duty must be on a housekeeper. + * If the current timer CPU is not a housekeeper, or no duty is assigned, + * pick the first housekeeper and assign it. + */ + if (tick_nohz_full_running) { + int timer_cpu = READ_ONCE(tick_do_timer_cpu); + if (timer_cpu == TICK_DO_TIMER_NONE || + !cpumask_test_cpu(timer_cpu, upd->new_mask)) { + int next_timer = cpumask_first(upd->new_mask); + if (next_timer < nr_cpu_ids) + WRITE_ONCE(tick_do_timer_cpu, next_timer); + } + } + + /* Kick all CPUs again to apply new nohz full state */ + for_each_online_cpu(cpu) + tick_nohz_full_kick_cpu(cpu); + + free_cpumask_var(non_housekeeping_mask); + } + + return NOTIFY_OK; +} + +static struct notifier_block tick_nohz_housekeeping_nb = { + .notifier_call = tick_nohz_housekeeping_reconfigure, +}; + void __init tick_nohz_init(void) { int cpu, ret; - if (!tick_nohz_full_running) - return; - - /* - * Full dynticks uses IRQ work to drive the tick rescheduling on safe - * locking contexts. But then we need IRQ work to raise its own - * interrupts to avoid circular dependency on the tick. - */ - if (!arch_irq_work_has_interrupt()) { - pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support IRQ work self-IPIs\n"); - cpumask_clear(tick_nohz_full_mask); - tick_nohz_full_running = false; - return; + if (!tick_nohz_full_mask) { + if (!slab_is_available()) + alloc_bootmem_cpumask_var(&tick_nohz_full_mask); + else + zalloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL); } - if (IS_ENABLED(CONFIG_PM_SLEEP_SMP) && - !IS_ENABLED(CONFIG_PM_SLEEP_SMP_NONZERO_CPU)) { - cpu = smp_processor_id(); + housekeeping_register_notifier(&tick_nohz_housekeeping_nb); - if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) { - pr_warn("NO_HZ: Clearing %d from nohz_full range " - "for timekeeping\n", cpu); - cpumask_clear_cpu(cpu, tick_nohz_full_mask); + if (tick_nohz_full_running) { + /* + * Full dynticks uses IRQ work to drive the tick rescheduling on safe + * locking contexts. But then we need IRQ work to raise its own + * interrupts to avoid circular dependency on the tick. + */ + if (!arch_irq_work_has_interrupt()) { + pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support IRQ work self-IPIs\n"); + cpumask_clear(tick_nohz_full_mask); + tick_nohz_full_running = false; + goto out; } + + if (IS_ENABLED(CONFIG_PM_SLEEP_SMP) && + !IS_ENABLED(CONFIG_PM_SLEEP_SMP_NONZERO_CPU)) { + cpu = smp_processor_id(); + + if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) { + pr_warn("NO_HZ: Clearing %d from nohz_full range " + "for timekeeping\n", cpu); + cpumask_clear_cpu(cpu, tick_nohz_full_mask); + } + } + + pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n", + cpumask_pr_args(tick_nohz_full_mask)); } - for_each_cpu(cpu, tick_nohz_full_mask) +out: + for_each_possible_cpu(cpu) ct_cpu_track_user(cpu); ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "kernel/nohz:predown", NULL, tick_nohz_cpu_down); WARN_ON(ret < 0); - pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n", - cpumask_pr_args(tick_nohz_full_mask)); } #endif /* #ifdef CONFIG_NO_HZ_FULL */ @@ -1209,7 +1289,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) if (unlikely(report_idle_softirq())) return false; - if (tick_nohz_full_enabled()) { + if (tick_nohz_full_running) { int tick_cpu = READ_ONCE(tick_do_timer_cpu); /* -- 2.43.0
