2 files changed, 62 insertions, 0 deletions
diff --git a/kernel/irq/Makefile b/kernel/irq/Makefile
index 2ee42e95a3ce..1d3ee3169202 100644
--- a/kernel/irq/Makefile
+++ b/kernel/irq/Makefile
@@ -9,3 +9,4 @@ obj-$(CONFIG_GENERIC_IRQ_MIGRATION) += cpuhotplug.o
 obj-$(CONFIG_PM_SLEEP) += pm.o
 obj-$(CONFIG_GENERIC_MSI_IRQ) += msi.o
 obj-$(CONFIG_GENERIC_IRQ_IPI) += ipi.o
+obj-$(CONFIG_SMP) += affinity.o
diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
new file mode 100644
index 000000000000..f68959341c0f
--- /dev/null
+++ b/kernel/irq/affinity.c
@@ -0,0 +1,61 @@
+
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/cpu.h>
+
+static int get_first_sibling(unsigned int cpu)
+{
+	unsigned int ret;
+
+	ret = cpumask_first(topology_sibling_cpumask(cpu));
+	if (ret < nr_cpu_ids)
+		return ret;
+	return cpu;
+}
+
+/*
+ * Take a map of online CPUs and the number of available interrupt vectors
+ * and generate an output cpumask suitable for spreading MSI/MSI-X vectors
+ * so that they are distributed as good as possible around the CPUs.  If
+ * more vectors than CPUs are available we'll map one to each CPU,
+ * otherwise we map one to the first sibling of each socket.
+ *
+ * If there are more vectors than CPUs we will still only have one bit
+ * set per CPU, but interrupt code will keep on assigning the vectors from
+ * the start of the bitmap until we run out of vectors.
+ */
+struct cpumask *irq_create_affinity_mask(unsigned int *nr_vecs)
+{
+	struct cpumask *affinity_mask;
+	unsigned int max_vecs = *nr_vecs;
+
+	if (max_vecs == 1)
+		return NULL;
+
+	affinity_mask = kzalloc(cpumask_size(), GFP_KERNEL);
+	if (!affinity_mask) {
+		*nr_vecs = 1;
+		return NULL;
+	}
+
+	if (max_vecs >= num_online_cpus()) {
+		cpumask_copy(affinity_mask, cpu_online_mask);
+		*nr_vecs = num_online_cpus();
+	} else {
+		unsigned int vecs = 0, cpu;
+
+		for_each_online_cpu(cpu) {
+			if (cpu == get_first_sibling(cpu)) {
+				cpumask_set_cpu(cpu, affinity_mask);
+				vecs++;
+			}
+
+			if (--max_vecs == 0)
+				break;
+		}
+		*nr_vecs = vecs;
+	}
+
+	return affinity_mask;
+}