Some places can be optimized by caching the target CPU for single CPU
affinities. That avoids finding the single CPU in the effective affinity
mask. Provide infrastructure for that.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
---
 include/linux/irq.h |   17 +++++++++++++++++
 kernel/irq/manage.c |   14 ++++++++++----
 2 files changed, 27 insertions(+), 4 deletions(-)

--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -140,6 +140,8 @@ struct irq_domain;
  * @effective_affinity:	The effective IRQ affinity on SMP as some irq
  *			chips do not allow multi CPU destinations.
  *			A subset of @affinity.
+ * @target_cpu:		The target CPU when @effective_affinity contains
+ *			only a single CPU, IRQ_TARGET_MULTI_CPU otherwise
  * @msi_desc:		MSI descriptor
  * @ipi_offset:		Offset of first IPI target cpu in @affinity. Optional.
  */
@@ -155,6 +157,7 @@ struct irq_common_data {
 #endif
 #ifdef CONFIG_GENERIC_IRQ_EFFECTIVE_AFF_MASK
 	cpumask_var_t		effective_affinity;
+	unsigned int		target_cpu;
 #endif
 #ifdef CONFIG_GENERIC_IRQ_IPI
 	unsigned int		ipi_offset;
@@ -903,6 +906,8 @@ static inline const struct cpumask *irq_
 	return d ? irq_data_get_affinity_mask(d) : NULL;
 }
 
+#define IRQ_TARGET_MULTI_CPU	UINT_MAX
+
 #ifdef CONFIG_GENERIC_IRQ_EFFECTIVE_AFF_MASK
 static inline
 const struct cpumask *irq_data_get_effective_affinity_mask(struct irq_data *d)
@@ -914,6 +919,14 @@ static inline void irq_data_update_effec
 {
 	cpumask_copy(d->common->effective_affinity, m);
 }
+static inline unsigned int irq_data_get_single_target(struct irq_data *d)
+{
+	return d->common->target_cpu;
+}
+static inline void irq_data_set_single_target(struct irq_data *d, unsigned int cpu)
+{
+	d->common->target_cpu = cpu;
+}
 #else
 static inline void irq_data_update_effective_affinity(struct irq_data *d,
 						      const struct cpumask *m)
@@ -924,6 +937,10 @@ const struct cpumask *irq_data_get_effec
 {
 	return irq_data_get_affinity_mask(d);
 }
+static inline unsigned int irq_data_get_single_target(struct irq_data *d)
+{
+	return IRQ_TARGET_MULTI_CPU;
+}
 #endif
 
 static inline
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -217,11 +217,17 @@ static void irq_validate_effective_affin
 {
 	const struct cpumask *m = irq_data_get_effective_affinity_mask(data);
 	struct irq_chip *chip = irq_data_get_irq_chip(data);
+	unsigned int target = IRQ_TARGET_MULTI_CPU;
 
-	if (!cpumask_empty(m))
-		return;
-	pr_warn_once("irq_chip %s did not update eff. affinity mask of irq %u\n",
-		     chip->name, data->irq);
+	switch (cpumask_weight(m)) {
+	case 0:
+		pr_warn_once("irq_chip %s did not update eff. affinity mask of irq %u\n",
+			     chip->name, data->irq);
+		break;
+	case 1:
+		target = cpumask_first(m);
+	}
+	irq_data_set_single_target(data, target);
 }
 #else
 static inline void irq_validate_effective_affinity(struct irq_data *data) { }