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Message-ID: <1482735654.4476.62.camel@gmx.de>
Date: Mon, 26 Dec 2016 08:00:54 +0100
From: Mike Galbraith <efault@....de>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
linux-rt-users <linux-rt-users@...r.kernel.org>,
Steven Rostedt <rostedt@...dmis.org>
Subject: [rfc patch-rt] posix_cpu_timers: Kill hotplug cpu notifier
Shamelessly steal softirq.c thread initialization method.
Signed-off-by: Mike Galbraith <efault@....de>
---
include/linux/cpuhotplug.h | 1
kernel/time/posix-cpu-timers.c | 158 ++++++++++++++---------------------------
2 files changed, 56 insertions(+), 103 deletions(-)
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -20,6 +20,7 @@ enum cpuhp_state {
CPUHP_SLUB_DEAD,
CPUHP_MM_WRITEBACK_DEAD,
CPUHP_SOFTIRQ_DEAD,
+ CPUHP_POSIXCPUTMR_DEAD,
CPUHP_NET_MVNETA_DEAD,
CPUHP_CPUIDLE_DEAD,
CPUHP_ARM64_FPSIMD_DEAD,
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -13,6 +13,8 @@
#include <linux/random.h>
#include <linux/tick.h>
#include <linux/workqueue.h>
+#include <linux/smpboot.h>
+#include <linux/cpuhotplug.h>
/*
* Called after updating RLIMIT_CPU to run cpu timer and update
@@ -1220,62 +1222,36 @@ static void __run_posix_cpu_timers(struc
DEFINE_PER_CPU(struct task_struct *, posix_timer_task);
DEFINE_PER_CPU(struct task_struct *, posix_timer_tasklist);
-static int posix_cpu_timers_thread(void *data)
+static void posix_cpu_timers_thread(unsigned int cpu)
{
- int cpu = (long)data;
+ struct task_struct *tsk = NULL;
+ struct task_struct *next = NULL;
- BUG_ON(per_cpu(posix_timer_task,cpu) != current);
+ /* grab task list */
+ raw_local_irq_disable();
+ tsk = per_cpu(posix_timer_tasklist, cpu);
+ per_cpu(posix_timer_tasklist, cpu) = NULL;
+ raw_local_irq_enable();
+
+ /* Process task list */
+ while (tsk) {
+ /* save next */
+ next = tsk->posix_timer_list;
- while (!kthread_should_stop()) {
- struct task_struct *tsk = NULL;
- struct task_struct *next = NULL;
-
- if (cpu_is_offline(cpu))
- goto wait_to_die;
-
- /* grab task list */
- raw_local_irq_disable();
- tsk = per_cpu(posix_timer_tasklist, cpu);
- per_cpu(posix_timer_tasklist, cpu) = NULL;
- raw_local_irq_enable();
-
- /* its possible the list is empty, just return */
- if (!tsk) {
- set_current_state(TASK_INTERRUPTIBLE);
- schedule();
- __set_current_state(TASK_RUNNING);
- continue;
- }
-
- /* Process task list */
- while (1) {
- /* save next */
- next = tsk->posix_timer_list;
+ /* run the task timers, clear its ptr and
+ * unreference it
+ */
+ __run_posix_cpu_timers(tsk);
+ tsk->posix_timer_list = NULL;
+ put_task_struct(tsk);
- /* run the task timers, clear its ptr and
- * unreference it
- */
- __run_posix_cpu_timers(tsk);
- tsk->posix_timer_list = NULL;
- put_task_struct(tsk);
-
- /* check if this is the last on the list */
- if (next == tsk)
- break;
- tsk = next;
- }
+ /* check if this is the last on the list */
+ if (next == tsk)
+ break;
+ tsk = next;
}
- return 0;
-wait_to_die:
- /* Wait for kthread_stop */
- set_current_state(TASK_INTERRUPTIBLE);
- while (!kthread_should_stop()) {
- schedule();
- set_current_state(TASK_INTERRUPTIBLE);
- }
- __set_current_state(TASK_RUNNING);
- return 0;
+ return;
}
static inline int __fastpath_timer_check(struct task_struct *tsk)
@@ -1322,72 +1298,48 @@ void run_posix_cpu_timers(struct task_st
}
}
-/*
- * posix_cpu_thread_call - callback that gets triggered when a CPU is added.
- * Here we can start up the necessary migration thread for the new CPU.
- */
-static int posix_cpu_thread_call(struct notifier_block *nfb,
- unsigned long action, void *hcpu)
+static void posix_cpu_thread_setup(unsigned int cpu)
{
- int cpu = (long)hcpu;
- struct task_struct *p;
- struct sched_param param;
+ struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
- switch (action) {
- case CPU_UP_PREPARE:
- p = kthread_create(posix_cpu_timers_thread, hcpu,
- "posixcputmr/%d",cpu);
- if (IS_ERR(p))
- return NOTIFY_BAD;
- p->flags |= PF_NOFREEZE;
- kthread_bind(p, cpu);
- /* Must be high prio to avoid getting starved */
- param.sched_priority = MAX_RT_PRIO-1;
- sched_setscheduler(p, SCHED_FIFO, ¶m);
- per_cpu(posix_timer_task,cpu) = p;
- break;
- case CPU_ONLINE:
- /* Strictly unneccessary, as first user will wake it. */
- wake_up_process(per_cpu(posix_timer_task,cpu));
- break;
-#ifdef CONFIG_HOTPLUG_CPU
- case CPU_UP_CANCELED:
- /* Unbind it from offline cpu so it can run. Fall thru. */
- kthread_bind(per_cpu(posix_timer_task, cpu),
- cpumask_any(cpu_online_mask));
- kthread_stop(per_cpu(posix_timer_task,cpu));
- per_cpu(posix_timer_task,cpu) = NULL;
- break;
- case CPU_DEAD:
- kthread_stop(per_cpu(posix_timer_task,cpu));
- per_cpu(posix_timer_task,cpu) = NULL;
- break;
-#endif
- }
- return NOTIFY_OK;
+ current->flags |= PF_NOFREEZE;
+ sched_setscheduler(current, SCHED_FIFO, ¶m);
}
-/* Register at highest priority so that task migration (migrate_all_tasks)
- * happens before everything else.
- */
-static struct notifier_block posix_cpu_thread_notifier = {
- .notifier_call = posix_cpu_thread_call,
- .priority = 10
+static void posix_cpu_thread_cleanup(unsigned int cpu, bool online)
+{
+ struct sched_param param = { .sched_priority = 0 };
+
+ current->flags &= ~PF_NOFREEZE;
+ sched_setscheduler(current, SCHED_NORMAL, ¶m);
+}
+
+static int posix_cpu_thread_should_run(unsigned int cpu)
+{
+ return !!per_cpu(posix_timer_tasklist, cpu);
+}
+
+static struct smp_hotplug_thread posix_timer_threads = {
+ .store = &posix_timer_task,
+ .setup = posix_cpu_thread_setup,
+ .cleanup = posix_cpu_thread_cleanup,
+ .thread_should_run = posix_cpu_thread_should_run,
+ .thread_fn = posix_cpu_timers_thread,
+ .thread_comm = "posixcputmr/%u",
};
static int __init posix_cpu_thread_init(void)
{
- void *hcpu = (void *)(long)smp_processor_id();
- /* Start one for boot CPU. */
+ struct smp_hotplug_thread *t = &posix_timer_threads;
unsigned long cpu;
- /* init the per-cpu posix_timer_tasklets */
+ /* init the per-cpu posix_timer_tasklist */
for_each_possible_cpu(cpu)
per_cpu(posix_timer_tasklist, cpu) = NULL;
- posix_cpu_thread_call(&posix_cpu_thread_notifier, CPU_UP_PREPARE, hcpu);
- posix_cpu_thread_call(&posix_cpu_thread_notifier, CPU_ONLINE, hcpu);
- register_cpu_notifier(&posix_cpu_thread_notifier);
+ cpuhp_setup_state_nocalls(CPUHP_POSIXCPUTMR_DEAD, "posixcputmr:dead", NULL, NULL);
+ BUG_ON(smpboot_register_percpu_thread(t));
+
return 0;
}
early_initcall(posix_cpu_thread_init);
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