diff options
Diffstat (limited to 'kernel/rcu/tree.c')
| -rw-r--r-- | kernel/rcu/tree.c | 138 |
1 files changed, 125 insertions, 13 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 980ca3ca643f..8e290163505a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -51,6 +51,12 @@ #include <linux/tick.h> #include <linux/sysrq.h> #include <linux/kprobes.h> +#include <linux/gfp.h> +#include <linux/oom.h> +#include <linux/smpboot.h> +#include <linux/jiffies.h> +#include <linux/sched/isolation.h> +#include "../time/tick-internal.h" #include "tree.h" #include "rcu.h" @@ -92,6 +98,9 @@ struct rcu_state rcu_state = { /* Dump rcu_node combining tree at boot to verify correct setup. */ static bool dump_tree; module_param(dump_tree, bool, 0444); +/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */ +static bool use_softirq = 1; +module_param(use_softirq, bool, 0444); /* Control rcu_node-tree auto-balancing at boot time. */ static bool rcu_fanout_exact; module_param(rcu_fanout_exact, bool, 0444); @@ -2253,7 +2262,7 @@ void rcu_force_quiescent_state(void) EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); /* Perform RCU core processing work for the current CPU. */ -static __latent_entropy void rcu_core(struct softirq_action *unused) +static __latent_entropy void rcu_core(void) { unsigned long flags; struct rcu_data *rdp = raw_cpu_ptr(&rcu_data); @@ -2295,29 +2304,131 @@ static __latent_entropy void rcu_core(struct softirq_action *unused) trace_rcu_utilization(TPS("End RCU core")); } +static void rcu_core_si(struct softirq_action *h) +{ + rcu_core(); +} + +static void rcu_wake_cond(struct task_struct *t, int status) +{ + /* + * If the thread is yielding, only wake it when this + * is invoked from idle + */ + if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current))) + wake_up_process(t); +} + +static void invoke_rcu_core_kthread(void) +{ + struct task_struct *t; + unsigned long flags; + + local_irq_save(flags); + __this_cpu_write(rcu_data.rcu_cpu_has_work, 1); + t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task); + if (t != NULL && t != current) + rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status)); + local_irq_restore(flags); +} + /* - * Schedule RCU callback invocation. If the running implementation of RCU - * does not support RCU priority boosting, just do a direct call, otherwise - * wake up the per-CPU kernel kthread. Note that because we are running - * on the current CPU with softirqs disabled, the rcu_cpu_kthread_task - * cannot disappear out from under us. + * Do RCU callback invocation. Not that if we are running !use_softirq, + * we are already in the rcuc kthread. If callbacks are offloaded, then + * ->cblist is always empty, so we don't get here. Therefore, we only + * ever need to check for the scheduler being operational (some callbacks + * do wakeups, so we do need the scheduler). */ static void invoke_rcu_callbacks(struct rcu_data *rdp) { if (unlikely(!READ_ONCE(rcu_scheduler_fully_active))) return; - if (likely(!rcu_state.boost)) { - rcu_do_batch(rdp); - return; - } - invoke_rcu_callbacks_kthread(); + rcu_do_batch(rdp); } +/* + * Wake up this CPU's rcuc kthread to do RCU core processing. + */ static void invoke_rcu_core(void) { - if (cpu_online(smp_processor_id())) + if (!cpu_online(smp_processor_id())) + return; + if (use_softirq) raise_softirq(RCU_SOFTIRQ); + else + invoke_rcu_core_kthread(); +} + +static void rcu_cpu_kthread_park(unsigned int cpu) +{ + per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; +} + +static int rcu_cpu_kthread_should_run(unsigned int cpu) +{ + return __this_cpu_read(rcu_data.rcu_cpu_has_work); +} + +/* + * Per-CPU kernel thread that invokes RCU callbacks. This replaces + * the RCU softirq used in configurations of RCU that do not support RCU + * priority boosting. + */ +static void rcu_cpu_kthread(unsigned int cpu) +{ + unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status); + char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work); + int spincnt; + + for (spincnt = 0; spincnt < 10; spincnt++) { + trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); + local_bh_disable(); + *statusp = RCU_KTHREAD_RUNNING; + local_irq_disable(); + work = *workp; + *workp = 0; + local_irq_enable(); + if (work) + rcu_core(); + local_bh_enable(); + if (*workp == 0) { + trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); + *statusp = RCU_KTHREAD_WAITING; + return; + } + } + *statusp = RCU_KTHREAD_YIELDING; + trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); + schedule_timeout_interruptible(2); + trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); + *statusp = RCU_KTHREAD_WAITING; +} + +static struct smp_hotplug_thread rcu_cpu_thread_spec = { + .store = &rcu_data.rcu_cpu_kthread_task, + .thread_should_run = rcu_cpu_kthread_should_run, + .thread_fn = rcu_cpu_kthread, + .thread_comm = "rcuc/%u", + .setup = rcu_cpu_kthread_setup, + .park = rcu_cpu_kthread_park, +}; + +/* + * Spawn per-CPU RCU core processing kthreads. + */ +static int __init rcu_spawn_core_kthreads(void) +{ + int cpu; + + for_each_possible_cpu(cpu) + per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0; + if (!IS_ENABLED(CONFIG_RCU_BOOST) && use_softirq) + return 0; + WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), + "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__); + return 0; } +early_initcall(rcu_spawn_core_kthreads); /* * Handle any core-RCU processing required by a call_rcu() invocation. @@ -3355,7 +3466,8 @@ void __init rcu_init(void) rcu_init_one(); if (dump_tree) rcu_dump_rcu_node_tree(); - open_softirq(RCU_SOFTIRQ, rcu_core); + if (use_softirq) + open_softirq(RCU_SOFTIRQ, rcu_core_si); /* * We don't need protection against CPU-hotplug here because |