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authorIngo Molnar <mingo@kernel.org>2014-07-05 11:06:10 +0200
committerIngo Molnar <mingo@kernel.org>2014-07-05 11:06:10 +0200
commit51da9830d7a58c8f77127c622ee57d453c88af09 (patch)
tree85bd2caae0344f77f0afd5f9617a45855000b821
parent5d5e2b1bcbdc996e72815c03fdc5ea82c4642397 (diff)
parentd490b3e2c23369c6adfa183d18d9a24ced247797 (diff)
downloadop-kernel-dev-51da9830d7a58c8f77127c622ee57d453c88af09.zip
op-kernel-dev-51da9830d7a58c8f77127c622ee57d453c88af09.tar.gz
Merge branch 'timers/nohz' into sched/core
Merge these two, because upcoming patches will touch both areas. Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--include/linux/irq_work.h5
-rw-r--r--include/linux/tick.h9
-rw-r--r--kernel/irq_work.c76
-rw-r--r--kernel/sched/core.c22
-rw-r--r--kernel/sched/sched.h12
-rw-r--r--kernel/smp.c9
-rw-r--r--kernel/time/tick-sched.c10
7 files changed, 97 insertions, 46 deletions
diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index 19ae05d..bf9422c 100644
--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -33,6 +33,11 @@ void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *))
#define DEFINE_IRQ_WORK(name, _f) struct irq_work name = { .func = (_f), }
bool irq_work_queue(struct irq_work *work);
+
+#ifdef CONFIG_SMP
+bool irq_work_queue_on(struct irq_work *work, int cpu);
+#endif
+
void irq_work_run(void);
void irq_work_sync(struct irq_work *work);
diff --git a/include/linux/tick.h b/include/linux/tick.h
index b84773c..8a4987f 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -181,7 +181,13 @@ static inline bool tick_nohz_full_cpu(int cpu)
extern void tick_nohz_init(void);
extern void __tick_nohz_full_check(void);
-extern void tick_nohz_full_kick(void);
+extern void tick_nohz_full_kick_cpu(int cpu);
+
+static inline void tick_nohz_full_kick(void)
+{
+ tick_nohz_full_kick_cpu(smp_processor_id());
+}
+
extern void tick_nohz_full_kick_all(void);
extern void __tick_nohz_task_switch(struct task_struct *tsk);
#else
@@ -189,6 +195,7 @@ static inline void tick_nohz_init(void) { }
static inline bool tick_nohz_full_enabled(void) { return false; }
static inline bool tick_nohz_full_cpu(int cpu) { return false; }
static inline void __tick_nohz_full_check(void) { }
+static inline void tick_nohz_full_kick_cpu(int cpu) { }
static inline void tick_nohz_full_kick(void) { }
static inline void tick_nohz_full_kick_all(void) { }
static inline void __tick_nohz_task_switch(struct task_struct *tsk) { }
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index a82170e..4b0a890 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -16,11 +16,12 @@
#include <linux/tick.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
+#include <linux/smp.h>
#include <asm/processor.h>
-static DEFINE_PER_CPU(struct llist_head, irq_work_list);
-static DEFINE_PER_CPU(int, irq_work_raised);
+static DEFINE_PER_CPU(struct llist_head, raised_list);
+static DEFINE_PER_CPU(struct llist_head, lazy_list);
/*
* Claim the entry so that no one else will poke at it.
@@ -55,12 +56,34 @@ void __weak arch_irq_work_raise(void)
*/
}
+#ifdef CONFIG_SMP
/*
- * Enqueue the irq_work @entry unless it's already pending
+ * Enqueue the irq_work @work on @cpu unless it's already pending
* somewhere.
*
* Can be re-enqueued while the callback is still in progress.
*/
+bool irq_work_queue_on(struct irq_work *work, int cpu)
+{
+ /* All work should have been flushed before going offline */
+ WARN_ON_ONCE(cpu_is_offline(cpu));
+
+ /* Arch remote IPI send/receive backend aren't NMI safe */
+ WARN_ON_ONCE(in_nmi());
+
+ /* Only queue if not already pending */
+ if (!irq_work_claim(work))
+ return false;
+
+ if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
+ arch_send_call_function_single_ipi(cpu);
+
+ return true;
+}
+EXPORT_SYMBOL_GPL(irq_work_queue_on);
+#endif
+
+/* Enqueue the irq work @work on the current CPU */
bool irq_work_queue(struct irq_work *work)
{
/* Only queue if not already pending */
@@ -70,15 +93,13 @@ bool irq_work_queue(struct irq_work *work)
/* Queue the entry and raise the IPI if needed. */
preempt_disable();
- llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
-
- /*
- * If the work is not "lazy" or the tick is stopped, raise the irq
- * work interrupt (if supported by the arch), otherwise, just wait
- * for the next tick.
- */
- if (!(work->flags & IRQ_WORK_LAZY) || tick_nohz_tick_stopped()) {
- if (!this_cpu_cmpxchg(irq_work_raised, 0, 1))
+ /* If the work is "lazy", handle it from next tick if any */
+ if (work->flags & IRQ_WORK_LAZY) {
+ if (llist_add(&work->llnode, &__get_cpu_var(lazy_list)) &&
+ tick_nohz_tick_stopped())
+ arch_irq_work_raise();
+ } else {
+ if (llist_add(&work->llnode, &__get_cpu_var(raised_list)))
arch_irq_work_raise();
}
@@ -90,10 +111,11 @@ EXPORT_SYMBOL_GPL(irq_work_queue);
bool irq_work_needs_cpu(void)
{
- struct llist_head *this_list;
+ struct llist_head *raised, *lazy;
- this_list = &__get_cpu_var(irq_work_list);
- if (llist_empty(this_list))
+ raised = &__get_cpu_var(raised_list);
+ lazy = &__get_cpu_var(lazy_list);
+ if (llist_empty(raised) && llist_empty(lazy))
return false;
/* All work should have been flushed before going offline */
@@ -102,28 +124,18 @@ bool irq_work_needs_cpu(void)
return true;
}
-static void __irq_work_run(void)
+static void irq_work_run_list(struct llist_head *list)
{
unsigned long flags;
struct irq_work *work;
- struct llist_head *this_list;
struct llist_node *llnode;
+ BUG_ON(!irqs_disabled());
- /*
- * Reset the "raised" state right before we check the list because
- * an NMI may enqueue after we find the list empty from the runner.
- */
- __this_cpu_write(irq_work_raised, 0);
- barrier();
-
- this_list = &__get_cpu_var(irq_work_list);
- if (llist_empty(this_list))
+ if (llist_empty(list))
return;
- BUG_ON(!irqs_disabled());
-
- llnode = llist_del_all(this_list);
+ llnode = llist_del_all(list);
while (llnode != NULL) {
work = llist_entry(llnode, struct irq_work, llnode);
@@ -148,6 +160,12 @@ static void __irq_work_run(void)
}
}
+static void __irq_work_run(void)
+{
+ irq_work_run_list(&__get_cpu_var(raised_list));
+ irq_work_run_list(&__get_cpu_var(lazy_list));
+}
+
/*
* Run the irq_work entries on this cpu. Requires to be ran from hardirq
* context with local IRQs disabled.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3bdf01b..7f3063c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -684,10 +684,16 @@ static void wake_up_idle_cpu(int cpu)
static bool wake_up_full_nohz_cpu(int cpu)
{
+ /*
+ * We just need the target to call irq_exit() and re-evaluate
+ * the next tick. The nohz full kick at least implies that.
+ * If needed we can still optimize that later with an
+ * empty IRQ.
+ */
if (tick_nohz_full_cpu(cpu)) {
if (cpu != smp_processor_id() ||
tick_nohz_tick_stopped())
- smp_send_reschedule(cpu);
+ tick_nohz_full_kick_cpu(cpu);
return true;
}
@@ -734,10 +740,11 @@ bool sched_can_stop_tick(void)
rq = this_rq();
- /* Make sure rq->nr_running update is visible after the IPI */
- smp_rmb();
-
- /* More than one running task need preemption */
+ /*
+ * More than one running task need preemption.
+ * nr_running update is assumed to be visible
+ * after IPI is sent from wakers.
+ */
if (rq->nr_running > 1)
return false;
@@ -1568,9 +1575,7 @@ void scheduler_ipi(void)
*/
preempt_fold_need_resched();
- if (llist_empty(&this_rq()->wake_list)
- && !tick_nohz_full_cpu(smp_processor_id())
- && !got_nohz_idle_kick())
+ if (llist_empty(&this_rq()->wake_list) && !got_nohz_idle_kick())
return;
/*
@@ -1587,7 +1592,6 @@ void scheduler_ipi(void)
* somewhat pessimize the simple resched case.
*/
irq_enter();
- tick_nohz_full_check();
sched_ttwu_pending();
/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 31cc02e..eb85676 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1221,9 +1221,15 @@ static inline void add_nr_running(struct rq *rq, unsigned count)
#ifdef CONFIG_NO_HZ_FULL
if (prev_nr < 2 && rq->nr_running >= 2) {
if (tick_nohz_full_cpu(rq->cpu)) {
- /* Order rq->nr_running write against the IPI */
- smp_wmb();
- smp_send_reschedule(rq->cpu);
+ /*
+ * Tick is needed if more than one task runs on a CPU.
+ * Send the target an IPI to kick it out of nohz mode.
+ *
+ * We assume that IPI implies full memory barrier and the
+ * new value of rq->nr_running is visible on reception
+ * from the target.
+ */
+ tick_nohz_full_kick_cpu(rq->cpu);
}
}
#endif
diff --git a/kernel/smp.c b/kernel/smp.c
index 306f818..a1812d1 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -3,6 +3,7 @@
*
* (C) Jens Axboe <jens.axboe@oracle.com> 2008
*/
+#include <linux/irq_work.h>
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <linux/kernel.h>
@@ -210,6 +211,14 @@ void generic_smp_call_function_single_interrupt(void)
csd->func(csd->info);
csd_unlock(csd);
}
+
+ /*
+ * Handle irq works queued remotely by irq_work_queue_on().
+ * Smp functions above are typically synchronous so they
+ * better run first since some other CPUs may be busy waiting
+ * for them.
+ */
+ irq_work_run();
}
/*
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 6558b7a..3d63944 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -224,13 +224,15 @@ static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
};
/*
- * Kick the current CPU if it's full dynticks in order to force it to
+ * Kick the CPU if it's full dynticks in order to force it to
* re-evaluate its dependency on the tick and restart it if necessary.
*/
-void tick_nohz_full_kick(void)
+void tick_nohz_full_kick_cpu(int cpu)
{
- if (tick_nohz_full_cpu(smp_processor_id()))
- irq_work_queue(&__get_cpu_var(nohz_full_kick_work));
+ if (!tick_nohz_full_cpu(cpu))
+ return;
+
+ irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
}
static void nohz_full_kick_ipi(void *info)
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