[PATCH 0/6] cpuidle: Make cpuidle governor switchable to be the default behaviour

[PATCH 0/6] cpuidle: Make cpuidle governor switchable to be the default behaviour

[Hanjun Guo]

This is the formal patch set after the RFC v2 [0].

For now cpuidle governor can be switched via sysfs only when the
boot option "cpuidle_sysfs_switch" is passed, but it's useful
to switch the governor to adapt to different workloads, especially
after TEO and haltpoll governors were introduced.

Make cpuidle governor switchable to be the default behaviour by
removing the sysfs_switch and switch attributes, also update the
document as well.

Patch 1/6 and 2/6 are bugfix patch which can be triggered if the
governor name is 15 characters, it is not a 'real' bug for now as we
don't have such usecases, so we can merge them together via this
patchset.

Patch 3/6 and 4/6 are the functional update to make cpuidle governor
switchable to be the default behaviour.

Patch 5/6 and 6/6 are the document update.

Changes since RFC v2:
 - Remove sizeof(char) in patch 1/6;
 - Fix some minor typos;
 - Adding Review/Test/ACK tags.

[0]:https://patchwork.kernel.org/cover/11519511/

Hanjun Guo (6):
  cpuidle: sysfs: Fix the overlap for showing available governors
  cpuidle: sysfs: Accept governor name with 15 characters
  cpuidle: Make cpuidle governor switchable to be the default behaviour
  cpuidle: sysfs: Remove sysfs_switch and switch attributes
  Documentation: cpuidle: update the document
  Documentation: ABI: make current_governer_ro as a candidate for
    removal

 Documentation/ABI/obsolete/sysfs-cpuidle           |  9 ++++
 Documentation/ABI/testing/sysfs-devices-system-cpu | 24 ++++-----
 Documentation/admin-guide/pm/cpuidle.rst           | 20 ++++----
 Documentation/driver-api/pm/cpuidle.rst            |  5 +-
 drivers/cpuidle/sysfs.c                            | 58 ++++++----------------
 5 files changed, 45 insertions(+), 71 deletions(-)
 create mode 100644 Documentation/ABI/obsolete/sysfs-cpuidle

-- 
1.7.12.4

[PATCH 1/6] cpuidle: sysfs: Fix the overlap for showing available governors

[Hanjun Guo]

When showing the available governors, it's "%s " in scnprintf(),
not "%s", so if the governor name has 15 characters, it will
overlap with the later one, fix it by adding one more for the
size.

While we are at it, fix the minor coding style issue and remove
the "/sizeof(char)" since sizeof(char) always equals 1.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>
---
 drivers/cpuidle/sysfs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/cpuidle/sysfs.c b/drivers/cpuidle/sysfs.c
index d3ef1d7..477b05a 100644
--- a/drivers/cpuidle/sysfs.c
+++ b/drivers/cpuidle/sysfs.c
@@ -35,10 +35,10 @@ static ssize_t show_available_governors(struct device *dev,
 
 	mutex_lock(&cpuidle_lock);
 	list_for_each_entry(tmp, &cpuidle_governors, governor_list) {
-		if (i >= (ssize_t) ((PAGE_SIZE/sizeof(char)) -
-				    CPUIDLE_NAME_LEN - 2))
+		if (i >= (ssize_t) (PAGE_SIZE - (CPUIDLE_NAME_LEN + 2)))
 			goto out;
-		i += scnprintf(&buf[i], CPUIDLE_NAME_LEN, "%s ", tmp->name);
+
+		i += scnprintf(&buf[i], CPUIDLE_NAME_LEN + 1, "%s ", tmp->name);
 	}
 
 out:
-- 
1.7.12.4

Re: [PATCH 1/6] cpuidle: sysfs: Fix the overlap for showing available governors

[Rafael J. Wysocki]

On Tue, May 19, 2020 at 8:32 AM Hanjun Guo <guohanjun@huawei.com> wrote:
>
> When showing the available governors, it's "%s " in scnprintf(),
> not "%s", so if the governor name has 15 characters, it will
> overlap with the later one, fix it by adding one more for the
> size.
>
> While we are at it, fix the minor coding style issue and remove
> the "/sizeof(char)" since sizeof(char) always equals 1.
>
> Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
> Reviewed-by: Doug Smythies <dsmythies@telus.net>
> Tested-by: Doug Smythies <dsmythies@telus.net>

All patches in this series applied as 5.8 material, thanks!

[PATCH 2/6] cpuidle: sysfs: Accept governor name with 15 characters

[Hanjun Guo]

CPUIDLE_NAME_LEN is 16, so it's possible to accept governor name
with 15 characters, but now store_current_governor() rejects
governor name with 15 characters as it returns -EINVAL if count
equals CPUIDLE_NAME_LEN.

Refactor the code to accept such case and simplify the code.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>
---
 drivers/cpuidle/sysfs.c | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/drivers/cpuidle/sysfs.c b/drivers/cpuidle/sysfs.c
index 477b05a..a57ad10 100644
--- a/drivers/cpuidle/sysfs.c
+++ b/drivers/cpuidle/sysfs.c
@@ -85,34 +85,25 @@ static ssize_t store_current_governor(struct device *dev,
 				      struct device_attribute *attr,
 				      const char *buf, size_t count)
 {
-	char gov_name[CPUIDLE_NAME_LEN];
-	int ret = -EINVAL;
-	size_t len = count;
+	char gov_name[CPUIDLE_NAME_LEN + 1];
+	int ret;
 	struct cpuidle_governor *gov;
 
-	if (!len || len >= sizeof(gov_name))
+	ret = sscanf(buf, "%" __stringify(CPUIDLE_NAME_LEN) "s", gov_name);
+	if (ret != 1)
 		return -EINVAL;
 
-	memcpy(gov_name, buf, len);
-	gov_name[len] = '\0';
-	if (gov_name[len - 1] == '\n')
-		gov_name[--len] = '\0';
-
 	mutex_lock(&cpuidle_lock);
-
+	ret = -EINVAL;
 	list_for_each_entry(gov, &cpuidle_governors, governor_list) {
-		if (strlen(gov->name) == len && !strcmp(gov->name, gov_name)) {
+		if (!strncmp(gov->name, gov_name, CPUIDLE_NAME_LEN)) {
 			ret = cpuidle_switch_governor(gov);
 			break;
 		}
 	}
-
 	mutex_unlock(&cpuidle_lock);
 
-	if (ret)
-		return ret;
-	else
-		return count;
+	return ret ? ret : count;
 }
 
 static DEVICE_ATTR(current_driver, 0444, show_current_driver, NULL);
-- 
1.7.12.4

[PATCH 3/6] cpuidle: Make cpuidle governor switchable to be the default behaviour

[Hanjun Guo]

For now cpuidle governor can be switched via sysfs only when the
boot option "cpuidle_sysfs_switch" is passed, but it's important
to switch the governor to adapt to different workloads, especially
after TEO and haltpoll governor were introduced.

Add available_governors and current_governor into the default
attributes, but reserve the current_governor_ro for compatiblity.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
 drivers/cpuidle/sysfs.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/cpuidle/sysfs.c b/drivers/cpuidle/sysfs.c
index a57ad10..b51c470d 100644
--- a/drivers/cpuidle/sysfs.c
+++ b/drivers/cpuidle/sysfs.c
@@ -106,19 +106,20 @@ static ssize_t store_current_governor(struct device *dev,
 	return ret ? ret : count;
 }
 
+static DEVICE_ATTR(available_governors, 0444, show_available_governors, NULL);
 static DEVICE_ATTR(current_driver, 0444, show_current_driver, NULL);
+static DEVICE_ATTR(current_governor, 0644, show_current_governor,
+				   store_current_governor);
 static DEVICE_ATTR(current_governor_ro, 0444, show_current_governor, NULL);
 
 static struct attribute *cpuidle_default_attrs[] = {
+	&dev_attr_available_governors.attr,
 	&dev_attr_current_driver.attr,
+	&dev_attr_current_governor.attr,
 	&dev_attr_current_governor_ro.attr,
 	NULL
 };
 
-static DEVICE_ATTR(available_governors, 0444, show_available_governors, NULL);
-static DEVICE_ATTR(current_governor, 0644, show_current_governor,
-		   store_current_governor);
-
 static struct attribute *cpuidle_switch_attrs[] = {
 	&dev_attr_available_governors.attr,
 	&dev_attr_current_driver.attr,
-- 
1.7.12.4

[PATCH 4/6] cpuidle: sysfs: Remove sysfs_switch and switch attributes

[Hanjun Guo]

Since the cpuidle governor can be switched via sysfs in default,
remove sysfs_switch and cpuidle_switch_attrs.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
 drivers/cpuidle/sysfs.c | 22 ++--------------------
 1 file changed, 2 insertions(+), 20 deletions(-)

diff --git a/drivers/cpuidle/sysfs.c b/drivers/cpuidle/sysfs.c
index b51c470d..14c0eb5 100644
--- a/drivers/cpuidle/sysfs.c
+++ b/drivers/cpuidle/sysfs.c
@@ -18,14 +18,6 @@
 
 #include "cpuidle.h"
 
-static unsigned int sysfs_switch;
-static int __init cpuidle_sysfs_setup(char *unused)
-{
-	sysfs_switch = 1;
-	return 1;
-}
-__setup("cpuidle_sysfs_switch", cpuidle_sysfs_setup);
-
 static ssize_t show_available_governors(struct device *dev,
 					struct device_attribute *attr,
 					char *buf)
@@ -112,7 +104,7 @@ static DEVICE_ATTR(current_governor, 0644, show_current_governor,
 				   store_current_governor);
 static DEVICE_ATTR(current_governor_ro, 0444, show_current_governor, NULL);
 
-static struct attribute *cpuidle_default_attrs[] = {
+static struct attribute *cpuidle_attrs[] = {
 	&dev_attr_available_governors.attr,
 	&dev_attr_current_driver.attr,
 	&dev_attr_current_governor.attr,
@@ -120,15 +112,8 @@ static DEVICE_ATTR(current_governor, 0644, show_current_governor,
 	NULL
 };
 
-static struct attribute *cpuidle_switch_attrs[] = {
-	&dev_attr_available_governors.attr,
-	&dev_attr_current_driver.attr,
-	&dev_attr_current_governor.attr,
-	NULL
-};
-
 static struct attribute_group cpuidle_attr_group = {
-	.attrs = cpuidle_default_attrs,
+	.attrs = cpuidle_attrs,
 	.name = "cpuidle",
 };
 
@@ -138,9 +123,6 @@ static DEVICE_ATTR(current_governor, 0644, show_current_governor,
  */
 int cpuidle_add_interface(struct device *dev)
 {
-	if (sysfs_switch)
-		cpuidle_attr_group.attrs = cpuidle_switch_attrs;
-
 	return sysfs_create_group(&dev->kobj, &cpuidle_attr_group);
 }
 
-- 
1.7.12.4

[PATCH 5/6] Documentation: cpuidle: update the document

[Hanjun Guo]

Update the document after the remove of cpuidle_sysfs_switch.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Doug Smythies <dsmythies@telus.net>
---
 Documentation/ABI/testing/sysfs-devices-system-cpu | 24 ++++++++--------------
 Documentation/admin-guide/pm/cpuidle.rst           | 20 ++++++++----------
 Documentation/driver-api/pm/cpuidle.rst            |  5 ++---
 3 files changed, 20 insertions(+), 29 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 2e0e3b4..6b5dafa 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -106,10 +106,10 @@ Description:	CPU topology files that describe a logical CPU's relationship
 		See Documentation/admin-guide/cputopology.rst for more information.
 
 
-What:		/sys/devices/system/cpu/cpuidle/current_driver
-		/sys/devices/system/cpu/cpuidle/current_governer_ro
-		/sys/devices/system/cpu/cpuidle/available_governors
+What:		/sys/devices/system/cpu/cpuidle/available_governors
+		/sys/devices/system/cpu/cpuidle/current_driver
 		/sys/devices/system/cpu/cpuidle/current_governor
+		/sys/devices/system/cpu/cpuidle/current_governer_ro
 Date:		September 2007
 Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
 Description:	Discover cpuidle policy and mechanism
@@ -119,24 +119,18 @@ Description:	Discover cpuidle policy and mechanism
 		consumption during idle.
 
 		Idle policy (governor) is differentiated from idle mechanism
-		(driver)
-
-		current_driver: (RO) displays current idle mechanism
-
-		current_governor_ro: (RO) displays current idle policy
-
-		With the cpuidle_sysfs_switch boot option enabled (meant for
-		developer testing), the following three attributes are visible
-		instead:
-
-		current_driver: same as described above
+		(driver).
 
 		available_governors: (RO) displays a space separated list of
-		available governors
+		available governors.
+
+		current_driver: (RO) displays current idle mechanism.
 
 		current_governor: (RW) displays current idle policy. Users can
 		switch the governor at runtime by writing to this file.
 
+		current_governor_ro: (RO) displays current idle policy.
+
 		See Documentation/admin-guide/pm/cpuidle.rst and
 		Documentation/driver-api/pm/cpuidle.rst for more information.
 
diff --git a/Documentation/admin-guide/pm/cpuidle.rst b/Documentation/admin-guide/pm/cpuidle.rst
index 5605cc6..a96a423 100644
--- a/Documentation/admin-guide/pm/cpuidle.rst
+++ b/Documentation/admin-guide/pm/cpuidle.rst
@@ -159,17 +159,15 @@ governor uses that information depends on what algorithm is implemented by it
 and that is the primary reason for having more than one governor in the
 ``CPUIdle`` subsystem.
 
-There are three ``CPUIdle`` governors available, ``menu``, `TEO <teo-gov_>`_
-and ``ladder``.  Which of them is used by default depends on the configuration
-of the kernel and in particular on whether or not the scheduler tick can be
-`stopped by the idle loop <idle-cpus-and-tick_>`_.  It is possible to change the
-governor at run time if the ``cpuidle_sysfs_switch`` command line parameter has
-been passed to the kernel, but that is not safe in general, so it should not be
-done on production systems (that may change in the future, though).  The name of
-the ``CPUIdle`` governor currently used by the kernel can be read from the
-:file:`current_governor_ro` (or :file:`current_governor` if
-``cpuidle_sysfs_switch`` is present in the kernel command line) file under
-:file:`/sys/devices/system/cpu/cpuidle/` in ``sysfs``.
+There are four ``CPUIdle`` governors available, ``menu``, `TEO <teo-gov_>`_,
+``ladder`` and ``haltpoll``.  Which of them is used by default depends on the
+configuration of the kernel and in particular on whether or not the scheduler
+tick can be `stopped by the idle loop <idle-cpus-and-tick_>`_.  Available
+governors can be read from the :file:`available_governors`, and the governor
+can be changed at runtime.  The name of the ``CPUIdle`` governor currently
+used by the kernel can be read from the :file:`current_governor_ro` or
+:file:`current_governor` file under :file:`/sys/devices/system/cpu/cpuidle/`
+in ``sysfs``.
 
 Which ``CPUIdle`` driver is used, on the other hand, usually depends on the
 platform the kernel is running on, but there are platforms with more than one
diff --git a/Documentation/driver-api/pm/cpuidle.rst b/Documentation/driver-api/pm/cpuidle.rst
index 006cf6d..3588bf0 100644
--- a/Documentation/driver-api/pm/cpuidle.rst
+++ b/Documentation/driver-api/pm/cpuidle.rst
@@ -68,9 +68,8 @@ only one in the list (that is, the list was empty before) or the value of its
 governor currently in use, or the name of the new governor was passed to the
 kernel as the value of the ``cpuidle.governor=`` command line parameter, the new
 governor will be used from that point on (there can be only one ``CPUIdle``
-governor in use at a time).  Also, if ``cpuidle_sysfs_switch`` is passed to the
-kernel in the command line, user space can choose the ``CPUIdle`` governor to
-use at run time via ``sysfs``.
+governor in use at a time).  Also, user space can choose the ``CPUIdle``
+governor to use at run time via ``sysfs``.
 
 Once registered, ``CPUIdle`` governors cannot be unregistered, so it is not
 practical to put them into loadable kernel modules.
-- 
1.7.12.4

[PATCH 6/6] Documentation: ABI: make current_governer_ro as a candidate for removal

[Hanjun Guo]

Since both current_governor and current_governor_ro co-exist under
/sys/devices/system/cpu/cpuidle/ file, and it's duplicate,
make current_governer_ro as a candidate for removal.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Doug Smythies <dsmythies@telus.net>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
 Documentation/ABI/obsolete/sysfs-cpuidle | 9 +++++++++
 1 file changed, 9 insertions(+)
 create mode 100644 Documentation/ABI/obsolete/sysfs-cpuidle

diff --git a/Documentation/ABI/obsolete/sysfs-cpuidle b/Documentation/ABI/obsolete/sysfs-cpuidle
new file mode 100644
index 00000000..e398fb5
--- /dev/null
+++ b/Documentation/ABI/obsolete/sysfs-cpuidle
@@ -0,0 +1,9 @@
+What:		/sys/devices/system/cpu/cpuidle/current_governor_ro
+Date:		April, 2020
+Contact:	linux-pm@vger.kernel.org
+Description:
+	current_governor_ro shows current using cpuidle governor, but read only.
+	with the update that cpuidle governor can be changed at runtime in default,
+	both current_governor and current_governor_ro co-exist under
+	/sys/devices/system/cpu/cpuidle/ file, it's duplicate so make
+	current_governor_ro obselete.
-- 
1.7.12.4

Re: [PATCH 0/6] cpuidle: Make cpuidle governor switchable to be the default behaviour

[Hanjun Guo]

On 2020/5/19 14:25, Hanjun Guo wrote:
> This is the formal patch set after the RFC v2 [0].
> 
> For now cpuidle governor can be switched via sysfs only when the
> boot option "cpuidle_sysfs_switch" is passed, but it's useful
> to switch the governor to adapt to different workloads, especially
> after TEO and haltpoll governors were introduced.
> 
> Make cpuidle governor switchable to be the default behaviour by
> removing the sysfs_switch and switch attributes, also update the
> document as well.
> 
> Patch 1/6 and 2/6 are bugfix patch which can be triggered if the
> governor name is 15 characters, it is not a 'real' bug for now as we
> don't have such usecases, so we can merge them together via this
> patchset.
> 
> Patch 3/6 and 4/6 are the functional update to make cpuidle governor
> switchable to be the default behaviour.
> 
> Patch 5/6 and 6/6 are the document update.
> 
> Changes since RFC v2:
>   - Remove sizeof(char) in patch 1/6;
>   - Fix some minor typos;
>   - Adding Review/Test/ACK tags.

Forgot to mention that this patch set is rebased on linux-next
branch of linux-pm.git

Thanks
Hanjun