lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list] 
Message-ID: <20251121100315.316300-2-ulf.hansson@linaro.org>
Date: Fri, 21 Nov 2025 11:03:07 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: "Rafael J . Wysocki" <rafael@...nel.org>,
	linux-pm@...r.kernel.org
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Kevin Hilman <khilman@...libre.com>,
	Pavel Machek <pavel@...nel.org>,
	Len Brown <len.brown@...el.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Maulik Shah <quic_mkshah@...cinc.com>,
	Prasad Sodagudi <psodagud@...cinc.com>,
	Dhruva Gole <d-gole@...com>,
	Deepti Jaggi <quic_djaggi@...cinc.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3 1/6] PM: QoS: Introduce a CPU system wakeup QoS limit

Some platforms supports multiple low power states for CPUs that can be used
when entering system-wide suspend. Currently we are always selecting the
deepest possible state for the CPUs, which can break the system wakeup
latency constraint that may be required for a use case.

Let's take the first step towards addressing this problem, by introducing
an interface for user space, that allows us to specify the CPU system
wakeup QoS limit. Subsequent changes will start taking into account the new
QoS limit.

Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
---

Changes in v3:
	- Add Kconfig for the new interface (Rafael).
	- Updated commit message.

Changes in v2:
	- Renamings to reflect the QoS are limited to CPUs.
	- Move code inside "CONFIG_CPU_IDLE".
---
 include/linux/pm_qos.h |   9 ++++
 kernel/power/Kconfig   |   4 ++
 kernel/power/qos.c     | 106 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 119 insertions(+)

diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
index 4a69d4af3ff8..6cea4455f867 100644
--- a/include/linux/pm_qos.h
+++ b/include/linux/pm_qos.h
@@ -162,6 +162,15 @@ static inline void cpu_latency_qos_update_request(struct pm_qos_request *req,
 static inline void cpu_latency_qos_remove_request(struct pm_qos_request *req) {}
 #endif
 
+#ifdef CONFIG_PM_QOS_CPU_SYSTEM_WAKEUP
+s32 cpu_wakeup_latency_qos_limit(void);
+#else
+static inline s32 cpu_wakeup_latency_qos_limit(void)
+{
+	return PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+}
+#endif
+
 #ifdef CONFIG_PM
 enum pm_qos_flags_status __dev_pm_qos_flags(struct device *dev, s32 mask);
 enum pm_qos_flags_status dev_pm_qos_flags(struct device *dev, s32 mask);
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 54a623680019..839e2dbb889e 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -202,6 +202,10 @@ config PM_WAKELOCKS_GC
 	depends on PM_WAKELOCKS
 	default y
 
+config PM_QOS_CPU_SYSTEM_WAKEUP
+	bool "User space interface for CPU system wakeup QoS"
+	depends on CPU_IDLE
+
 config PM
 	bool "Device power management core functionality"
 	help
diff --git a/kernel/power/qos.c b/kernel/power/qos.c
index 4244b069442e..f7d8064e9adc 100644
--- a/kernel/power/qos.c
+++ b/kernel/power/qos.c
@@ -415,6 +415,105 @@ static struct miscdevice cpu_latency_qos_miscdev = {
 	.fops = &cpu_latency_qos_fops,
 };
 
+#ifdef CONFIG_PM_QOS_CPU_SYSTEM_WAKEUP
+/* The CPU system wakeup latency QoS. */
+static struct pm_qos_constraints cpu_wakeup_latency_constraints = {
+	.list = PLIST_HEAD_INIT(cpu_wakeup_latency_constraints.list),
+	.target_value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT,
+	.default_value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT,
+	.no_constraint_value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT,
+	.type = PM_QOS_MIN,
+};
+
+/**
+ * cpu_wakeup_latency_qos_limit - Current CPU system wakeup latency QoS limit.
+ *
+ * Returns the current CPU system wakeup latency QoS limit that may have been
+ * requested by user space.
+ */
+s32 cpu_wakeup_latency_qos_limit(void)
+{
+	return pm_qos_read_value(&cpu_wakeup_latency_constraints);
+}
+
+static int cpu_wakeup_latency_qos_open(struct inode *inode, struct file *filp)
+{
+	struct pm_qos_request *req;
+
+	req = kzalloc(sizeof(*req), GFP_KERNEL);
+	if (!req)
+		return -ENOMEM;
+
+	req->qos = &cpu_wakeup_latency_constraints;
+	pm_qos_update_target(req->qos, &req->node, PM_QOS_ADD_REQ,
+			     PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);
+	filp->private_data = req;
+
+	return 0;
+}
+
+static int cpu_wakeup_latency_qos_release(struct inode *inode,
+					  struct file *filp)
+{
+	struct pm_qos_request *req = filp->private_data;
+
+	filp->private_data = NULL;
+	pm_qos_update_target(req->qos, &req->node, PM_QOS_REMOVE_REQ,
+			     PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);
+	kfree(req);
+
+	return 0;
+}
+
+static ssize_t cpu_wakeup_latency_qos_read(struct file *filp, char __user *buf,
+					   size_t count, loff_t *f_pos)
+{
+	s32 value = pm_qos_read_value(&cpu_wakeup_latency_constraints);
+
+	return simple_read_from_buffer(buf, count, f_pos, &value, sizeof(s32));
+}
+
+static ssize_t cpu_wakeup_latency_qos_write(struct file *filp,
+					    const char __user *buf,
+					    size_t count, loff_t *f_pos)
+{
+	struct pm_qos_request *req = filp->private_data;
+	s32 value;
+
+	if (count == sizeof(s32)) {
+		if (copy_from_user(&value, buf, sizeof(s32)))
+			return -EFAULT;
+	} else {
+		int ret;
+
+		ret = kstrtos32_from_user(buf, count, 16, &value);
+		if (ret)
+			return ret;
+	}
+
+	if (value < 0)
+		return -EINVAL;
+
+	pm_qos_update_target(req->qos, &req->node, PM_QOS_UPDATE_REQ, value);
+
+	return count;
+}
+
+static const struct file_operations cpu_wakeup_latency_qos_fops = {
+	.open = cpu_wakeup_latency_qos_open,
+	.release = cpu_wakeup_latency_qos_release,
+	.read = cpu_wakeup_latency_qos_read,
+	.write = cpu_wakeup_latency_qos_write,
+	.llseek = noop_llseek,
+};
+
+static struct miscdevice cpu_wakeup_latency_qos_miscdev = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "cpu_wakeup_latency",
+	.fops = &cpu_wakeup_latency_qos_fops,
+};
+#endif /* CONFIG_PM_QOS_CPU_SYSTEM_WAKEUP */
+
 static int __init cpu_latency_qos_init(void)
 {
 	int ret;
@@ -424,6 +523,13 @@ static int __init cpu_latency_qos_init(void)
 		pr_err("%s: %s setup failed\n", __func__,
 		       cpu_latency_qos_miscdev.name);
 
+#ifdef CONFIG_PM_QOS_CPU_SYSTEM_WAKEUP
+	ret = misc_register(&cpu_wakeup_latency_qos_miscdev);
+	if (ret < 0)
+		pr_err("%s: %s setup failed\n", __func__,
+		       cpu_wakeup_latency_qos_miscdev.name);
+#endif
+
 	return ret;
 }
 late_initcall(cpu_latency_qos_init);
-- 
2.43.0

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ