show nohz_full cpus in sysfs

Currently there is no way to query which CPUs are in nohz_full
mode from userspace.

Export the CPU list running in nohz_full mode in sysfs,
specifically in the file /sys/devices/system/cpu/nohz_full

This can be used by system management tools like libvirt,
openstack, and others to ensure proper task placement.

Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Acked-by: Chris Metcalf <cmetcalf@ezchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index ea23ee7..78720e7 100644 (file)
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -16,6 +16,7 @@
 #include <linux/acpi.h>
 #include <linux/of.h>
 #include <linux/cpufeature.h>
+#include <linux/tick.h>
 
 #include "base.h"
 
@@ -276,6 +277,19 @@ static ssize_t print_cpus_isolated(struct device *dev,
 }
 static DEVICE_ATTR(isolated, 0444, print_cpus_isolated, NULL);
 
+#ifdef CONFIG_NO_HZ_FULL
+static ssize_t print_cpus_nohz_full(struct device *dev,
+                                 struct device_attribute *attr, char *buf)
+{
+       int n = 0, len = PAGE_SIZE-2;
+
+       n = scnprintf(buf, len, "%*pbl\n", cpumask_pr_args(tick_nohz_full_mask));
+
+       return n;
+}
+static DEVICE_ATTR(nohz_full, 0444, print_cpus_nohz_full, NULL);
+#endif
+
 static void cpu_device_release(struct device *dev)
 {
        /*
@@ -443,6 +457,9 @@ static struct attribute *cpu_root_attrs[] = {
        &dev_attr_kernel_max.attr,
        &dev_attr_offline.attr,
        &dev_attr_isolated.attr,
+#ifdef CONFIG_NO_HZ_FULL
+       &dev_attr_nohz_full.attr,
+#endif
 #ifdef CONFIG_GENERIC_CPU_AUTOPROBE
        &dev_attr_modalias.attr,
 #endif