[PATCH, v6 3/3] cgroups: introduce timer slack controller

["Kirill A. Shutsemov" <kirill@shutemov.name>]

From: Kirill A. Shutemov <kirill@shutemov.name>

Every task_struct has timer_slack_ns value. This value uses to round up
poll() and select() timeout values. This feature can be useful in
mobile environment where combined wakeups are desired.

cgroup subsys "timer_slack" implement timer slack controller. It
provides a way to group tasks by timer slack value and manage the
value of group's tasks.

Idea-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 Documentation/cgroups/timer_slack.txt |   93 +++++++++++
 include/linux/cgroup_subsys.h         |    6 +
 init/Kconfig                          |   10 ++
 kernel/Makefile                       |    1 +
 kernel/cgroup_timer_slack.c           |  285 +++++++++++++++++++++++++++++++++
 5 files changed, 395 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/cgroups/timer_slack.txt
 create mode 100644 kernel/cgroup_timer_slack.c

diff --git a/Documentation/cgroups/timer_slack.txt b/Documentation/cgroups/timer_slack.txt
new file mode 100644
index 0000000..e7ec2f3
--- /dev/null
+++ b/Documentation/cgroups/timer_slack.txt
@@ -0,0 +1,93 @@
+Timer Slack Controller
+=====================
+
+Overview
+--------
+
+Every task_struct has timer_slack_ns value. This value uses to round up
+poll() and select() timeout values. This feature can be useful in
+mobile environment where combined wakeups are desired.
+
+cgroup subsys "timer_slack" implement timer slack controller. It
+provides a way to group tasks by timer slack value and manage the
+value of group's tasks.
+
+
+User interface
+--------------
+
+To get timer slack controller functionality you need to enable it in
+kernel configuration:
+
+CONFIG_CGROUP_TIMER_SLACK=y
+
+or if you want to compile it as module:
+
+CONFIG_CGROUP_TIMER_SLACK=m
+
+The controller provides three files in cgroup directory:
+
+# mount -t cgroup -o timer_slack none /sys/fs/cgroup
+# ls /sys/fs/cgroup/timer_slack.*
+/sys/fs/cgroup/timer_slack.max_slack_ns
+/sys/fs/cgroup/timer_slack.min_slack_ns
+/sys/fs/cgroup/timer_slack.set_slack_ns
+
+timer_slack.min_slack_ns and timer_slack.set_slack_ns specify allowed
+range of timer slack for tasks in cgroup. By default it unlimited:
+
+# cat /sys/fs/cgroup/timer_slack.min_slack_ns
+0
+# cat /sys/fs/cgroup/timer_slack.max_slack_ns
+4294967295
+
+You can specify limits you want:
+
+# echo 50000 > /sys/fs/cgroup/timer_slack.min_slack_ns
+# echo 1000000 > /sys/fs/cgroup/timer_slack.max_slack_ns
+# cat /sys/fs/cgroup/timer_slack.{min,max}_slack_ns
+50000
+1000000
+
+Timer slack value of all tasks of the cgroup will be adjusted to fit
+min-max range.
+
+If a task will try to call prctl() to change timer slack value out of
+the range it get -EPERM.
+
+You can change timer slack value of all tasks of the cgroup at once:
+
+# echo 70000 > /sys/fs/cgroup/timer_slack.set_slack_ns
+
+Timer slack controller supports hierarchical groups. The only rule:
+parent's limit range should be wider or equal to child's. Sibling
+cgroups can have overlapping min-max range.
+
+		(root: 50000 - 1000000)
+		 /		     \
+	(a: 50000 - 50000)	(b: 500000 - 1000000)
+				 /		   \
+			(c: 500000 - 900000) (d: 700000 - 800000)
+
+# mkdir /sys/fs/cgroup/a
+# echo 50000 > /sys/fs/cgroup/a/timer_slack.max_slack_ns
+# cat /sys/fs/cgroup/a/timer_slack.{min,max}_slack_ns
+50000
+50000
+# mkdir /sys/fs/cgroup/b
+# echo 500000 > /sys/fs/cgroup/b/timer_slack.min_slack_ns
+# cat /sys/fs/cgroup/b/timer_slack.{min,max}_slack_ns
+500000
+1000000
+# mkdir /sys/fs/cgroup/b/c
+# echo 900000 > /sys/fs/cgroup/b/c/timer_slack.max_slack_ns
+# cat /sys/fs/cgroup/b/c/timer_slack.{min,max}_slack_ns
+500000
+900000
+# mkdir /sys/fs/cgroup/b/d
+# echo 700000 > /sys/fs/cgroup/b/d/timer_slack.min_slack_ns
+# echo 800000 > /sys/fs/cgroup/b/d/timer_slack.max_slack_ns
+# cat /sys/fs/cgroup/b/d/timer_slack.{min,max}_slack_ns
+700000
+800000
+
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index ccefff0..e399228 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -66,3 +66,9 @@ SUBSYS(blkio)
 #endif
 
 /* */
+
+#ifdef CONFIG_CGROUP_TIMER_SLACK
+SUBSYS(timer_slack)
+#endif
+
+/* */
diff --git a/init/Kconfig b/init/Kconfig
index be788c0..bb54ae9 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -596,6 +596,16 @@ config CGROUP_FREEZER
 	  Provides a way to freeze and unfreeze all tasks in a
 	  cgroup.
 
+config CGROUP_TIMER_SLACK
+	tristate "Timer slack cgroup controller"
+	help
+	  Provides a way of tasks grouping by timer slack value.
+	  Every timer slack cgroup has min and max slack value. Task's
+	  timer slack value will be adjusted to fit min-max range once
+	  the task attached to the cgroup.
+	  It's useful in mobile devices where certain background apps
+	  are attached to a cgroup and combined wakeups are desired.
+
 config CGROUP_DEVICE
 	bool "Device controller for cgroups"
 	help
diff --git a/kernel/Makefile b/kernel/Makefile
index aa43e63..0e660c5 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -61,6 +61,7 @@ obj-$(CONFIG_BACKTRACE_SELF_TEST) += backtracetest.o
 obj-$(CONFIG_COMPAT) += compat.o
 obj-$(CONFIG_CGROUPS) += cgroup.o
 obj-$(CONFIG_CGROUP_FREEZER) += cgroup_freezer.o
+obj-$(CONFIG_CGROUP_TIMER_SLACK) += cgroup_timer_slack.o
 obj-$(CONFIG_CPUSETS) += cpuset.o
 obj-$(CONFIG_CGROUP_NS) += ns_cgroup.o
 obj-$(CONFIG_UTS_NS) += utsname.o
diff --git a/kernel/cgroup_timer_slack.c b/kernel/cgroup_timer_slack.c
new file mode 100644
index 0000000..ec63700
--- /dev/null
+++ b/kernel/cgroup_timer_slack.c
@@ -0,0 +1,285 @@
+/*
+ * cgroup_timer_slack.c - control group timer slack subsystem
+ *
+ * Copyright Nokia Corparation, 2011
+ * Author: Kirill A. Shutemov
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+#include <linux/cgroup.h>
+#include <linux/init_task.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/rcupdate.h>
+
+struct cgroup_subsys timer_slack_subsys;
+struct timer_slack_cgroup {
+	struct cgroup_subsys_state css;
+	unsigned long min_slack_ns;
+	unsigned long max_slack_ns;
+};
+
+enum {
+	TIMER_SLACK_MIN,
+	TIMER_SLACK_MAX,
+};
+
+static struct timer_slack_cgroup *cgroup_to_tslack_cgroup(struct cgroup *cgroup)
+{
+	struct cgroup_subsys_state *css;
+
+	css = cgroup_subsys_state(cgroup, timer_slack_subsys.subsys_id);
+	return container_of(css, struct timer_slack_cgroup, css);
+}
+
+static int is_timer_slack_allowed(struct timer_slack_cgroup *tslack_cgroup,
+		unsigned long slack_ns)
+{
+	if (slack_ns < tslack_cgroup->min_slack_ns ||
+			slack_ns > tslack_cgroup->max_slack_ns)
+		return false;
+	return true;
+}
+
+static int cgroup_timer_slack_check(struct notifier_block *nb,
+		unsigned long slack_ns, void *data)
+{
+	struct cgroup_subsys_state *css;
+	struct timer_slack_cgroup *tslack_cgroup;
+
+	/* XXX: lockdep false positive? */
+	rcu_read_lock();
+	css = task_subsys_state(current, timer_slack_subsys.subsys_id);
+	tslack_cgroup = container_of(css, struct timer_slack_cgroup, css);
+	rcu_read_unlock();
+
+	if (!is_timer_slack_allowed(tslack_cgroup, slack_ns))
+		return notifier_from_errno(-EPERM);
+	return NOTIFY_OK;
+}
+
+static struct notifier_block cgroup_timer_slack_nb = {
+	.notifier_call = cgroup_timer_slack_check,
+};
+
+static struct cgroup_subsys_state *
+tslack_cgroup_create(struct cgroup_subsys *subsys, struct cgroup *cgroup)
+{
+	struct timer_slack_cgroup *tslack_cgroup;
+
+	tslack_cgroup = kmalloc(sizeof(*tslack_cgroup), GFP_KERNEL);
+	if (!tslack_cgroup)
+		return ERR_PTR(-ENOMEM);
+
+	if (cgroup->parent) {
+		struct timer_slack_cgroup *parent;
+		parent = cgroup_to_tslack_cgroup(cgroup->parent);
+		tslack_cgroup->min_slack_ns = parent->min_slack_ns;
+		tslack_cgroup->max_slack_ns = parent->max_slack_ns;
+	} else {
+		tslack_cgroup->min_slack_ns = 0UL;
+		tslack_cgroup->max_slack_ns = ULONG_MAX;
+	}
+
+	return &tslack_cgroup->css;
+}
+
+static void tslack_cgroup_destroy(struct cgroup_subsys *subsys,
+		struct cgroup *cgroup)
+{
+	kfree(cgroup_to_tslack_cgroup(cgroup));
+}
+
+/*
+ * Adjust ->timer_slack_ns and ->default_max_slack_ns of the task to fit
+ * limits of the cgroup.
+ */
+static void tslack_adjust_task(struct timer_slack_cgroup *tslack_cgroup,
+		struct task_struct *tsk)
+{
+	if (tslack_cgroup->min_slack_ns > tsk->timer_slack_ns)
+		tsk->timer_slack_ns = tslack_cgroup->min_slack_ns;
+	else if (tslack_cgroup->max_slack_ns < tsk->timer_slack_ns)
+		tsk->timer_slack_ns = tslack_cgroup->max_slack_ns;
+
+	if (tslack_cgroup->min_slack_ns > tsk->default_timer_slack_ns)
+		tsk->default_timer_slack_ns = tslack_cgroup->min_slack_ns;
+	else if (tslack_cgroup->max_slack_ns < tsk->default_timer_slack_ns)
+		tsk->default_timer_slack_ns = tslack_cgroup->max_slack_ns;
+}
+
+static void tslack_cgroup_attach(struct cgroup_subsys *subsys,
+		struct cgroup *cgroup, struct cgroup *prev,
+		struct task_struct *tsk, bool threadgroup)
+{
+	tslack_adjust_task(cgroup_to_tslack_cgroup(cgroup), tsk);
+}
+
+static int tslack_write_set_slack_ns(struct cgroup *cgroup, struct cftype *cft,
+		u64 val)
+{
+	struct timer_slack_cgroup *tslack_cgroup;
+	struct cgroup_iter it;
+	struct task_struct *task;
+
+	tslack_cgroup = cgroup_to_tslack_cgroup(cgroup);
+	if (!is_timer_slack_allowed(cgroup_to_tslack_cgroup(cgroup), val))
+		return -EPERM;
+
+	/* Change timer slack value for all tasks in the cgroup */
+	cgroup_iter_start(cgroup, &it);
+	while ((task = cgroup_iter_next(cgroup, &it)))
+		task->timer_slack_ns = val;
+	cgroup_iter_end(cgroup, &it);
+
+	return 0;
+}
+
+static u64 tslack_read_range(struct cgroup *cgroup, struct cftype *cft)
+{
+	struct timer_slack_cgroup *tslack_cgroup;
+
+	tslack_cgroup = cgroup_to_tslack_cgroup(cgroup);
+	switch (cft->private) {
+	case TIMER_SLACK_MIN:
+		return tslack_cgroup->min_slack_ns;
+	case TIMER_SLACK_MAX:
+		return tslack_cgroup->max_slack_ns;
+	default:
+		BUG();
+	}
+}
+
+static int validate_change(struct cgroup *cgroup, u64 val, int type)
+{
+	struct timer_slack_cgroup *tslack_cgroup, *child;
+	struct cgroup *cur;
+
+	BUG_ON(type != TIMER_SLACK_MIN && type != TIMER_SLACK_MAX);
+
+	if (val > ULONG_MAX)
+		return -EINVAL;
+
+	if (cgroup->parent) {
+		struct timer_slack_cgroup *parent;
+		parent = cgroup_to_tslack_cgroup(cgroup->parent);
+		if (!is_timer_slack_allowed(parent, val))
+			return -EPERM;
+	}
+
+	tslack_cgroup = cgroup_to_tslack_cgroup(cgroup);
+	if (type == TIMER_SLACK_MIN && val > tslack_cgroup->max_slack_ns)
+		return -EINVAL;
+	if (type == TIMER_SLACK_MAX && val < tslack_cgroup->min_slack_ns)
+		return -EINVAL;
+
+	list_for_each_entry(cur, &cgroup->children, sibling) {
+		child = cgroup_to_tslack_cgroup(cur);
+		if (type == TIMER_SLACK_MIN && val > child->min_slack_ns)
+			return -EBUSY;
+		if (type == TIMER_SLACK_MAX && val < child->max_slack_ns)
+			return -EBUSY;
+	}
+
+	return 0;
+}
+
+static int tslack_write_range(struct cgroup *cgroup, struct cftype *cft,
+		u64 val)
+{
+	struct timer_slack_cgroup *tslack_cgroup;
+	struct cgroup_iter it;
+	struct task_struct *task;
+	int err;
+
+	err = validate_change(cgroup, val, cft->private);
+	if (err)
+		return err;
+
+	tslack_cgroup = cgroup_to_tslack_cgroup(cgroup);
+	if (cft->private == TIMER_SLACK_MIN)
+		tslack_cgroup->min_slack_ns = val;
+	else
+		tslack_cgroup->max_slack_ns = val;
+
+	/*
+	 * Adjust timer slack value for all tasks in the cgroup to fit
+	 * min-max range.
+	 */
+	cgroup_iter_start(cgroup, &it);
+	while ((task = cgroup_iter_next(cgroup, &it)))
+		tslack_adjust_task(tslack_cgroup, task);
+	cgroup_iter_end(cgroup, &it);
+
+	return 0;
+}
+
+static struct cftype files[] = {
+	{
+		.name = "set_slack_ns",
+		.write_u64 = tslack_write_set_slack_ns,
+	},
+	{
+		.name = "min_slack_ns",
+		.private = TIMER_SLACK_MIN,
+		.read_u64 = tslack_read_range,
+		.write_u64 = tslack_write_range,
+	},
+	{
+		.name = "max_slack_ns",
+		.private = TIMER_SLACK_MAX,
+		.read_u64 = tslack_read_range,
+		.write_u64 = tslack_write_range,
+	},
+};
+
+static int tslack_cgroup_populate(struct cgroup_subsys *subsys,
+		struct cgroup *cgroup)
+{
+	return cgroup_add_files(cgroup, subsys, files, ARRAY_SIZE(files));
+}
+
+struct cgroup_subsys timer_slack_subsys = {
+	.name = "timer_slack",
+	.module = THIS_MODULE,
+#ifndef CONFIG_CGROUP_TIMER_SLACK_MODULE
+	.subsys_id = timer_slack_subsys_id,
+#endif
+	.create = tslack_cgroup_create,
+	.destroy = tslack_cgroup_destroy,
+	.attach = tslack_cgroup_attach,
+	.populate = tslack_cgroup_populate,
+};
+
+static int __init init_cgroup_timer_slack(void)
+{
+	int err;
+
+	err = register_timer_slack_notifier(&cgroup_timer_slack_nb);
+	if (err)
+		return err;
+
+	err = cgroup_load_subsys(&timer_slack_subsys);
+	if (err)
+		unregister_timer_slack_notifier(&cgroup_timer_slack_nb);
+
+	return err;
+}
+
+static void __exit exit_cgroup_timer_slack(void)
+{
+	unregister_timer_slack_notifier(&cgroup_timer_slack_nb);
+	cgroup_unload_subsys(&timer_slack_subsys);
+}
+
+module_init(init_cgroup_timer_slack);
+module_exit(exit_cgroup_timer_slack);
+MODULE_LICENSE("GPL");
-- 
1.7.4