[PATCH v7 03/12] sysfs: Add preferred CPU file
From: Shrikanth Hegde <hidden>
Date: 2026-07-09 21:58:12
Also in:
lkml
Subsystem:
driver core, kobjects, debugfs and sysfs, the rest · Maintainers:
Greg Kroah-Hartman, "Rafael J. Wysocki", Danilo Krummrich, Linus Torvalds
Add "preferred" file in /sys/devices/system/cpu
This offers
- User can quickly check which CPUs are marked as preferred at this
moment.
- Userspace algorithms irqbalance could use this mask to send irq 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 <redacted>
---
Documentation/ABI/testing/sysfs-devices-system-cpu | 11 +++++++++++
drivers/base/cpu.c | 8 ++++++++
2 files changed, 19 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 82d10d556cc8..ac1dbb209cc7 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu@@ -806,3 +806,14 @@ 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: July 2026 +Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> +Description: + (RO) the list of preferred CPUs at this moment. + These are the only CPUs meant to be used at the moment. + Using CPU outside of the list could lead to more + contention of underlying physical CPU resource. Dynamically + changes based on steal time. With CONFIG_PREFERRED_CPU=n it + is same as active CPUs. See sched-arch.rst for more details.
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 19d288a3c80c..4ac990efee7c 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c@@ -391,6 +391,13 @@ static int cpu_uevent(const struct device *dev, struct kobj_uevent_env *env) } #endif +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); + const struct bus_type cpu_subsys = { .name = "cpu", .dev_name = "cpu",
@@ -532,6 +539,7 @@ static struct attribute *cpu_root_attrs[] = { #ifdef CONFIG_GENERIC_CPU_AUTOPROBE &dev_attr_modalias.attr, #endif + &dev_attr_preferred.attr, NULL };
--
2.47.3