[RFC][PATCH 2/2] cpuidle: Allow idle states to be disabled by default

Rafael J. Wysocki
2019-11-18T23:10:10Z

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

In certain situations it may be useful to prevent some idle states
from being used by default while allowing user space to enable them
later on.

For this purpose, introduce a new state flag, CPUIDLE_FLAG_UNCERTAIN,
to mark idle states that should be disabled by default, make the
core set CPUIDLE_STATE_DISABLED_BY_USER for those states at the
initialization time and add a new state attribute in sysfs,
"disable_default", to provide user space with the default value
of the "disable" attribute (1 if CPUIDLE_FLAG_UNCERTAIN is set for
the given state, 0 otherwise) to allow it to restore the initial
configuration of idle states easily if need be.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
Documentation/ABI/testing/sysfs-devices-system-cpu | 6 ++++++
Documentation/admin-guide/pm/cpuidle.rst | 3 +++
drivers/cpuidle/cpuidle.c | 3 +++
drivers/cpuidle/sysfs.c | 9 +++++++++
include/linux/cpuidle.h | 1 +
5 files changed, 22 insertions(+)

Index: linux-pm/drivers/cpuidle/sysfs.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/sysfs.c
+++ linux-pm/drivers/cpuidle/sysfs.c
@@ -327,6 +327,13 @@ static ssize_t store_state_disable(struc
return size;
}

+static ssize_t show_state_disable_default(struct cpuidle_state *state,
+ struct cpuidle_state_usage *state_usage,
+ char *buf)
+{
+ return sprintf(buf, "%u\n", !!(state->flags & CPUIDLE_FLAG_UNCERTAIN));
+}
+
define_one_state_ro(name, show_state_name);
define_one_state_ro(desc, show_state_desc);
define_one_state_ro(latency, show_state_exit_latency);
@@ -337,6 +344,7 @@ define_one_state_ro(time, show_state_tim
define_one_state_rw(disable, show_state_disable, store_state_disable);
define_one_state_ro(above, show_state_above);
define_one_state_ro(below, show_state_below);
+define_one_state_ro(disable_default, show_state_disable_default);

static struct attribute *cpuidle_state_default_attrs[] = {
&attr_name.attr,
@@ -347,6 +355,7 @@ static struct attribute *cpuidle_state_d
&attr_usage.attr,
&attr_time.attr,
&attr_disable.attr,
+ &attr_disable_default.attr,
&attr_above.attr,
&attr_below.attr,
NULL
Index: linux-pm/include/linux/cpuidle.h
===================================================================
--- linux-pm.orig/include/linux/cpuidle.h
+++ linux-pm/include/linux/cpuidle.h
@@ -77,6 +77,7 @@ struct cpuidle_state {
#define CPUIDLE_FLAG_COUPLED BIT(1) /* state applies to multiple cpus */
#define CPUIDLE_FLAG_TIMER_STOP BIT(2) /* timer is stopped on this state */
#define CPUIDLE_FLAG_UNUSABLE BIT(3) /* avoid using this state */
+#define CPUIDLE_FLAG_UNCERTAIN BIT(4) /* disable this state by default */

struct cpuidle_device_kobj;
struct cpuidle_state_kobj;
Index: linux-pm/drivers/cpuidle/cpuidle.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/cpuidle.c
+++ linux-pm/drivers/cpuidle/cpuidle.c
@@ -572,6 +572,9 @@ static int __cpuidle_register_device(str
for (i = 0; i < drv->state_count; i++) {
if (drv->states[i].flags & CPUIDLE_FLAG_UNUSABLE)
dev->states_usage[i].disable |= CPUIDLE_STATE_DISABLED_BY_DRIVER;
+
+ if (drv->states[i].flags & CPUIDLE_FLAG_UNCERTAIN)
+ dev->states_usage[i].disable |= CPUIDLE_STATE_DISABLED_BY_USER;
}

per_cpu(cpuidle_devices, dev->cpu) = dev;
Index: linux-pm/Documentation/ABI/testing/sysfs-devices-system-cpu
===================================================================
--- linux-pm.orig/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ linux-pm/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -196,6 +196,12 @@ Description:
does not reflect it. Likewise, if one enables a deep state but a
lighter state still is disabled, then this has no effect.

+What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/disable_dafault
+Date: November 2019
+KernelVersion: v5.4
+Contact: Linux power management list <linux-pm@vger.kernel.org>
+Description:
+ (RO) The default value of the disable state attribute (bool).

What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/residency
Date: March 2014
Index: linux-pm/Documentation/admin-guide/pm/cpuidle.rst
===================================================================
--- linux-pm.orig/Documentation/admin-guide/pm/cpuidle.rst
+++ linux-pm/Documentation/admin-guide/pm/cpuidle.rst
@@ -506,6 +506,9 @@ object corresponding to it, as follows:
``disable``
Whether or not this idle state is disabled.

+``disable_default``
+ The default value of the ``disable`` attribute.
+
``latency``
Exit latency of the idle state in microseconds.