[PATCH v11 04/12] sysfs: Add preferred CPU file
flat view
COLD35d
From: Shrikanth Hegde <sshegde@linux.ibm.com>
Date: 2026-08-25 10:40:32
Also in:
linux-doc, lkml
Subsystem:
driver core, kobjects, debugfs and sysfs, the rest · Maintainers:
Greg Kroah-Hartman, "Rafael J. Wysocki", Danilo Krummrich, Linus Torvalds
Revision v11 of 6 in this series.
Revisions (6)
Add a "preferred" file in /sys/devices/system/cpu/ when kernel is
built with CONFIG_PREFERRED_CPU=y.
This would help
- Users to quickly check which CPUs are marked as preferred.
- Userspace daemons such as irqbalance to use this mask to
route irqs into preferred CPUs.
For example:
cat /sys/devices/system/cpu/online
0-719
cat /sys/devices/system/cpu/preferred
0-599 <<< Implies 0-599 are preferred for workloads and 600-719
should be avoided at this moment.
cat /sys/devices/system/cpu/preferred
0-719 <<< All CPUs are usable. There is no preference.
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
Documentation/ABI/testing/sysfs-devices-system-cpu | 14 ++++++++++++++
drivers/base/cpu.c | 12 ++++++++++++
2 files changed, 26 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 82d10d556cc8..080c69aca4f0 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu@@ -806,3 +806,17 @@ Date: Nov 2022 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> Description: (RO) the list of CPUs that can be brought online. + +What: /sys/devices/system/cpu/preferred +Date: Aug 2026 +Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> +Description: + (RO) the list of preferred CPUs applicable in + paravirtualized environments. + + The steal governor driver dynamically adjusts this mask + based on observed steal time. Scheduling tasks on + CPUs outside of this list may lead to performance + degradations due to underlying physical CPU contention. + + See Documentation/scheduler/sched-paravirt.rst for more details.
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 19d288a3c80c..5da2a96fb37e 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c@@ -391,6 +391,15 @@ static int cpu_uevent(const struct device *dev, struct kobj_uevent_env *env) } #endif +#ifdef CONFIG_PREFERRED_CPU +static ssize_t preferred_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(cpu_preferred_mask)); +} +static DEVICE_ATTR_RO(preferred); +#endif + const struct bus_type cpu_subsys = { .name = "cpu", .dev_name = "cpu",
@@ -531,6 +540,9 @@ static struct attribute *cpu_root_attrs[] = { #endif #ifdef CONFIG_GENERIC_CPU_AUTOPROBE &dev_attr_modalias.attr, +#endif +#ifdef CONFIG_PREFERRED_CPU + &dev_attr_preferred.attr, #endif NULL };
--
2.47.3