Merge branch 'timers/nohz-irq-work-v7' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into timers/nohz

Pull nohz updates from Frederic Weisbecker:

 " This set moves the nohz kick, used to notify a full dynticks CPU when
   events require tick rescheduling, out of the scheduler tick to a
   dedicated IPI.

   This debloats a bit the scheduler IPI from off-topic work that was
   abusing that scheduler fast path for its convenient asynchronous
   properties. Now the nohz kick uses irq-work for its own needs.

   Of course this implied quite some background infrastructure rework,
   including:

     * Clean up some irq-work internals
     * Implement remote irq-work
     * Implement nohz kick on top of remote irq-work
     * Move full dynticks timer enqueue notification to new kick
     * Move multi-task notification to new kick
     * Remove unecessary barriers on multi-task notification
 "

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 47 insertions, 29 deletions

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index a82170e2fa78..4b0a890a304a 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.