[PATCH 1/2] show isolated cpus in sysfs

[riel]

From: Rik van Riel <riel@xxxxxxxxxx>

After system bootup, there is no totally reliable way to see
which CPUs are isolated, because the kernel may modify the
CPUs specified on the isolcpus= kernel command line option.

Export the CPU list that actually got isolated in sysfs,
specifically in the file /sys/devices/system/cpu/isolated

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

Suggested-by: Li Zefan <lizefan@xxxxxxxxxx>
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
---
 drivers/base/cpu.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index f160ea44a86d..ea23ee7b545b 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -265,6 +265,17 @@ static ssize_t print_cpus_offline(struct device *dev,
 }
 static DEVICE_ATTR(offline, 0444, print_cpus_offline, NULL);
 
+static ssize_t print_cpus_isolated(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(cpu_isolated_map));
+
+	return n;
+}
+static DEVICE_ATTR(isolated, 0444, print_cpus_isolated, NULL);
+
 static void cpu_device_release(struct device *dev)
 {
 	/*
@@ -431,6 +442,7 @@ static struct attribute *cpu_root_attrs[] = {
 	&cpu_attrs[2].attr.attr,
 	&dev_attr_kernel_max.attr,
 	&dev_attr_offline.attr,
+	&dev_attr_isolated.attr,
 #ifdef CONFIG_GENERIC_CPU_AUTOPROBE
 	&dev_attr_modalias.attr,
 #endif
-- 
2.1.0

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