[PATCH, v5 0/2] Timer slack cgroup subsystem

[PATCH, v5 0/2] Timer slack cgroup subsystem

[Kirill A. Shutsemov]

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

Changelog:
v5:
 - -EBUSY on writing to timer_slack.min_slack_ns/max_slack_ns if a child has
   wider min-max range
v4:
 - hierarchy support
 - drop dummy_timer_slack_check()
 - workaround lockdep false (?) positive
 - allow 0 as timer slack value
v3:
 - rework interface
 - s/EXPORT_SYMBOL/EXPORT_SYMBOL_GPL/
v2:
 - fixed with CONFIG_CGROUP_TIMER_SLACK=y
v1:
 - initial revision

Kirill A. Shutemov (2):
  cgroups: export cgroup_iter_{start,next,end}
  cgroups: introduce timer slack subsystem

 include/linux/cgroup_subsys.h |    6 +
 include/linux/init_task.h     |    4 +-
 init/Kconfig                  |   10 ++
 kernel/Makefile               |    1 +
 kernel/cgroup.c               |    3 +
 kernel/cgroup_timer_slack.c   |  281 +++++++++++++++++++++++++++++++++++++++++
 kernel/sys.c                  |   19 ++-
 7 files changed, 317 insertions(+), 7 deletions(-)
 create mode 100644 kernel/cgroup_timer_slack.c

-- 
1.7.4

[PATCH, v5 1/2] cgroups: export cgroup_iter_{start,next,end}

[Kirill A. Shutsemov]

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

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Acked-by: Paul Menage <menage@google.com>
---
 kernel/cgroup.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index b24d702..8234daa 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2443,6 +2443,7 @@ void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
 	it->cg_link = &cgrp->css_sets;
 	cgroup_advance_iter(cgrp, it);
 }
+EXPORT_SYMBOL_GPL(cgroup_iter_start);
 
 struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
 					struct cgroup_iter *it)
@@ -2467,11 +2468,13 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
 	}
 	return res;
 }
+EXPORT_SYMBOL_GPL(cgroup_iter_next);
 
 void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it)
 {
 	read_unlock(&css_set_lock);
 }
+EXPORT_SYMBOL_GPL(cgroup_iter_end);
 
 static inline int started_after_time(struct task_struct *t1,
 				     struct timespec *time,
-- 
1.7.4

Re: [PATCH, v5 1/2] cgroups: export cgroup_iter_{start,next,end}

[Balbir Singh]

* Kirill A. Shutsemov <kirill@shutemov.name> [2011-02-07 11:46:01]:

> From: Kirill A. Shutemov <kirill@shutemov.name>
> 
> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> Acked-by: Paul Menage <menage@google.com>


Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
 

-- 
	Three Cheers,
	Balbir

[PATCH, v5 2/2] cgroups: introduce timer slack subsystem

[Kirill A. Shutsemov]

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

Provides a way of tasks grouping by timer slack value. Introduces per
cgroup max and min timer slack value. When a task attaches to a cgroup,
its timer slack value adjusts (if needed) to fit min-max range.

It also provides a way to set timer slack value for all tasks in the
cgroup at once.

This functionality is useful in mobile devices where certain background
apps are attached to a cgroup and minimum wakeups are desired.

Idea-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 include/linux/cgroup_subsys.h |    6 +
 include/linux/init_task.h     |    4 +-
 init/Kconfig                  |   10 ++
 kernel/Makefile               |    1 +
 kernel/cgroup_timer_slack.c   |  281 +++++++++++++++++++++++++++++++++++++++++
 kernel/sys.c                  |   19 ++-
 6 files changed, 314 insertions(+), 7 deletions(-)
 create mode 100644 kernel/cgroup_timer_slack.c

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/include/linux/init_task.h b/include/linux/init_task.h
index caa151f..48eca8f 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -124,6 +124,8 @@ extern struct cred init_cred;
 # define INIT_PERF_EVENTS(tsk)
 #endif
 
+#define TIMER_SLACK_NS_DEFAULT 50000
+
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -177,7 +179,7 @@ extern struct cred init_cred;
 	.cpu_timers	= INIT_CPU_TIMERS(tsk.cpu_timers),		\
 	.fs_excl	= ATOMIC_INIT(0),				\
 	.pi_lock	= __RAW_SPIN_LOCK_UNLOCKED(tsk.pi_lock),	\
-	.timer_slack_ns = 50000, /* 50 usec default slack */		\
+	.timer_slack_ns = TIMER_SLACK_NS_DEFAULT,			\
 	.pids = {							\
 		[PIDTYPE_PID]  = INIT_PID_LINK(PIDTYPE_PID),		\
 		[PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID),		\
diff --git a/init/Kconfig b/init/Kconfig
index be788c0..6cf465f 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 subsystem"
+	help
+	  Provides a way of tasks grouping by timer slack value.
+	  Introduces per cgroup timer slack value which will override
+	  the default timer slack value once a task is attached to a
+	  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 353d3fe..0b60239 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..609e1f1
--- /dev/null
+++ b/kernel/cgroup_timer_slack.c
@@ -0,0 +1,281 @@
+/*
+ * 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,
+};
+
+extern int (*timer_slack_check)(struct task_struct *task,
+		unsigned long slack_ns);
+
+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 task_struct *task,
+		unsigned long slack_ns)
+{
+	struct cgroup_subsys_state *css;
+	struct timer_slack_cgroup *tslack_cgroup;
+
+	/* XXX: lockdep false positive? */
+	rcu_read_lock();
+	css = task_subsys_state(task, 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 -EPERM;
+	return 0;
+}
+
+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 (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;
+	else if (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;
+		else if (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,
+#ifdef CONFIG_CGROUP_TIMER_SLACK
+	.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;
+
+	if (timer_slack_check)
+		return -EBUSY;
+	timer_slack_check = cgroup_timer_slack_check;
+
+	err = cgroup_load_subsys(&timer_slack_subsys);
+	if (err)
+		timer_slack_check = NULL;
+	return err;
+}
+
+static void __exit exit_cgroup_timer_slack(void)
+{
+	BUG_ON(timer_slack_check != cgroup_timer_slack_check);
+	timer_slack_check = NULL;
+	cgroup_unload_subsys(&timer_slack_subsys);
+}
+
+module_init(init_cgroup_timer_slack);
+module_exit(exit_cgroup_timer_slack);
+MODULE_LICENSE("GPL");
diff --git a/kernel/sys.c b/kernel/sys.c
index 18da702..3bc4205 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -118,6 +118,10 @@ EXPORT_SYMBOL(cad_pid);
 
 void (*pm_power_off_prepare)(void);
 
+int (*timer_slack_check)(struct task_struct *task, unsigned long slack_ns) =
+	NULL;
+EXPORT_SYMBOL_GPL(timer_slack_check);
+
 /*
  * set the priority of a task
  * - the caller must hold the RCU read lock
@@ -1694,12 +1698,15 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			error = current->timer_slack_ns;
 			break;
 		case PR_SET_TIMERSLACK:
-			if (arg2 <= 0)
-				current->timer_slack_ns =
-					current->default_timer_slack_ns;
-			else
-				current->timer_slack_ns = arg2;
-			error = 0;
+			if (arg2 <= 0) {
+				me->timer_slack_ns = me->default_timer_slack_ns;
+				break;
+			}
+
+			error = timer_slack_check ?
+				timer_slack_check(me, arg2) : 0;
+			if (!error)
+				me->timer_slack_ns = arg2;
 			break;
 		case PR_MCE_KILL:
 			if (arg4 | arg5)
-- 
1.7.4

Re: [PATCH, v5 2/2] cgroups: introduce timer slack subsystem

[Balbir Singh]

* Kirill A. Shutsemov <kirill@shutemov.name> [2011-02-07 11:46:02]:

> From: Kirill A. Shutemov <kirill@shutemov.name>
> 
> Provides a way of tasks grouping by timer slack value. Introduces per
> cgroup max and min timer slack value. When a task attaches to a cgroup,
> its timer slack value adjusts (if needed) to fit min-max range.
> 
> It also provides a way to set timer slack value for all tasks in the
> cgroup at once.
> 
> This functionality is useful in mobile devices where certain background
> apps are attached to a cgroup and minimum wakeups are desired.
> 
> Idea-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> ---
>  include/linux/cgroup_subsys.h |    6 +
>  include/linux/init_task.h     |    4 +-
>  init/Kconfig                  |   10 ++
>  kernel/Makefile               |    1 +
>  kernel/cgroup_timer_slack.c   |  281 +++++++++++++++++++++++++++++++++++++++++
>  kernel/sys.c                  |   19 ++-
>  6 files changed, 314 insertions(+), 7 deletions(-)
>  create mode 100644 kernel/cgroup_timer_slack.c
> 
> 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/include/linux/init_task.h b/include/linux/init_task.h
> index caa151f..48eca8f 100644
> --- a/include/linux/init_task.h
> +++ b/include/linux/init_task.h
> @@ -124,6 +124,8 @@ extern struct cred init_cred;
>  # define INIT_PERF_EVENTS(tsk)
>  #endif
> 
> +#define TIMER_SLACK_NS_DEFAULT 50000
> +
>  /*
>   *  INIT_TASK is used to set up the first task table, touch at
>   * your own risk!. Base=0, limit=0x1fffff (=2MB)
> @@ -177,7 +179,7 @@ extern struct cred init_cred;
>  	.cpu_timers	= INIT_CPU_TIMERS(tsk.cpu_timers),		\
>  	.fs_excl	= ATOMIC_INIT(0),				\
>  	.pi_lock	= __RAW_SPIN_LOCK_UNLOCKED(tsk.pi_lock),	\
> -	.timer_slack_ns = 50000, /* 50 usec default slack */		\
> +	.timer_slack_ns = TIMER_SLACK_NS_DEFAULT,			\
>  	.pids = {							\
>  		[PIDTYPE_PID]  = INIT_PID_LINK(PIDTYPE_PID),		\
>  		[PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID),		\
> diff --git a/init/Kconfig b/init/Kconfig
> index be788c0..6cf465f 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 subsystem"
> +	help
> +	  Provides a way of tasks grouping by timer slack value.
> +	  Introduces per cgroup timer slack value which will override
> +	  the default timer slack value once a task is attached to a
> +	  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 353d3fe..0b60239 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..609e1f1
> --- /dev/null
> +++ b/kernel/cgroup_timer_slack.c
> @@ -0,0 +1,281 @@
> +/*
> + * 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,
> +};
> +
> +extern int (*timer_slack_check)(struct task_struct *task,
> +		unsigned long slack_ns);
> +
> +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 task_struct *task,
> +		unsigned long slack_ns)
> +{
> +	struct cgroup_subsys_state *css;
> +	struct timer_slack_cgroup *tslack_cgroup;
> +
> +	/* XXX: lockdep false positive? */
> +	rcu_read_lock();
> +	css = task_subsys_state(task, timer_slack_subsys.subsys_id);
> +	tslack_cgroup = container_of(css, struct timer_slack_cgroup, css);

Shouldn't the rcu_read_unlock() be after the check of is_timer_slack_allowed()?

> +	rcu_read_unlock();
> +
> +	if (!is_timer_slack_allowed(tslack_cgroup, slack_ns))
> +		return -EPERM;
> +	return 0;
> +}
> +
> +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);

OK, I've got questions, are the following possible

1. Assign a task to a cgroup based on timer slack, it is accepted
based on min and max values
2. We update the slack

Can't this be bad for some tasks, is there a way for a task to prevent
the max slack from being updated?

2. Can there be an overlap in the ranges?


-- 
	Three Cheers,
	Balbir

Re: [PATCH, v5 2/2] cgroups: introduce timer slack subsystem

[Kirill A. Shutemov]

On Mon, Feb 07, 2011 at 03:36:24PM +0530, Balbir Singh wrote:
> * Kirill A. Shutsemov <kirill@shutemov.name> [2011-02-07 11:46:02]:
> 
> > From: Kirill A. Shutemov <kirill@shutemov.name>
> > 
> > Provides a way of tasks grouping by timer slack value. Introduces per
> > cgroup max and min timer slack value. When a task attaches to a cgroup,
> > its timer slack value adjusts (if needed) to fit min-max range.
> > 
> > It also provides a way to set timer slack value for all tasks in the
> > cgroup at once.
> > 
> > This functionality is useful in mobile devices where certain background
> > apps are attached to a cgroup and minimum wakeups are desired.
> > 
> > Idea-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> > ---
> >  include/linux/cgroup_subsys.h |    6 +
> >  include/linux/init_task.h     |    4 +-
> >  init/Kconfig                  |   10 ++
> >  kernel/Makefile               |    1 +
> >  kernel/cgroup_timer_slack.c   |  281 +++++++++++++++++++++++++++++++++++++++++
> >  kernel/sys.c                  |   19 ++-
> >  6 files changed, 314 insertions(+), 7 deletions(-)
> >  create mode 100644 kernel/cgroup_timer_slack.c
> > 
> > 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/include/linux/init_task.h b/include/linux/init_task.h
> > index caa151f..48eca8f 100644
> > --- a/include/linux/init_task.h
> > +++ b/include/linux/init_task.h
> > @@ -124,6 +124,8 @@ extern struct cred init_cred;
> >  # define INIT_PERF_EVENTS(tsk)
> >  #endif
> > 
> > +#define TIMER_SLACK_NS_DEFAULT 50000
> > +
> >  /*
> >   *  INIT_TASK is used to set up the first task table, touch at
> >   * your own risk!. Base=0, limit=0x1fffff (=2MB)
> > @@ -177,7 +179,7 @@ extern struct cred init_cred;
> >  	.cpu_timers	= INIT_CPU_TIMERS(tsk.cpu_timers),		\
> >  	.fs_excl	= ATOMIC_INIT(0),				\
> >  	.pi_lock	= __RAW_SPIN_LOCK_UNLOCKED(tsk.pi_lock),	\
> > -	.timer_slack_ns = 50000, /* 50 usec default slack */		\
> > +	.timer_slack_ns = TIMER_SLACK_NS_DEFAULT,			\
> >  	.pids = {							\
> >  		[PIDTYPE_PID]  = INIT_PID_LINK(PIDTYPE_PID),		\
> >  		[PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID),		\
> > diff --git a/init/Kconfig b/init/Kconfig
> > index be788c0..6cf465f 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 subsystem"
> > +	help
> > +	  Provides a way of tasks grouping by timer slack value.
> > +	  Introduces per cgroup timer slack value which will override
> > +	  the default timer slack value once a task is attached to a
> > +	  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 353d3fe..0b60239 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..609e1f1
> > --- /dev/null
> > +++ b/kernel/cgroup_timer_slack.c
> > @@ -0,0 +1,281 @@
> > +/*
> > + * 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,
> > +};
> > +
> > +extern int (*timer_slack_check)(struct task_struct *task,
> > +		unsigned long slack_ns);
> > +
> > +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 task_struct *task,
> > +		unsigned long slack_ns)
> > +{
> > +	struct cgroup_subsys_state *css;
> > +	struct timer_slack_cgroup *tslack_cgroup;
> > +
> > +	/* XXX: lockdep false positive? */
> > +	rcu_read_lock();
> > +	css = task_subsys_state(task, timer_slack_subsys.subsys_id);
> > +	tslack_cgroup = container_of(css, struct timer_slack_cgroup, css);
> 
> Shouldn't the rcu_read_unlock() be after the check of is_timer_slack_allowed()?

I'm not sure if this rcu_read_lock() is needed. See freezer_fork().

> > +	rcu_read_unlock();
> > +
> > +	if (!is_timer_slack_allowed(tslack_cgroup, slack_ns))
> > +		return -EPERM;
> > +	return 0;
> > +}
> > +
> > +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);
> 
> OK, I've got questions, are the following possible
> 
> 1. Assign a task to a cgroup based on timer slack, it is accepted
> based on min and max values

Hm.. Currently, there is no such functionality. Do we need it? What's use
case?

> 2. We update the slack
> 
> Can't this be bad for some tasks, is there a way for a task to prevent
> the max slack from being updated?

If a non-RT task can't tolerate not being on time it's totally broken.
RT-tasks are not affected by timer slack.

And we believe that user knows what he does.

> 2. Can there be an overlap in the ranges?

What overlap do you mean?
There is only one rule: parent's range should be wider then child's.

-- 
 Kirill A. Shutemov

Re: [PATCH, v5 2/2] cgroups: introduce timer slack subsystem

[Balbir Singh]

* Kirill A. Shutemov <kirill@shutemov.name> [2011-02-07 12:57:30]:

> On Mon, Feb 07, 2011 at 03:36:24PM +0530, Balbir Singh wrote:
> > * Kirill A. Shutsemov <kirill@shutemov.name> [2011-02-07 11:46:02]:
> > 
> > > From: Kirill A. Shutemov <kirill@shutemov.name>
> > > 
> > > Provides a way of tasks grouping by timer slack value. Introduces per
> > > cgroup max and min timer slack value. When a task attaches to a cgroup,
> > > its timer slack value adjusts (if needed) to fit min-max range.
> > > 
> > > It also provides a way to set timer slack value for all tasks in the
> > > cgroup at once.
> > > 
> > > This functionality is useful in mobile devices where certain background
> > > apps are attached to a cgroup and minimum wakeups are desired.
> > > 
> > > Idea-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > > Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> > > ---
> > >  include/linux/cgroup_subsys.h |    6 +
> > >  include/linux/init_task.h     |    4 +-
> > >  init/Kconfig                  |   10 ++
> > >  kernel/Makefile               |    1 +
> > >  kernel/cgroup_timer_slack.c   |  281 +++++++++++++++++++++++++++++++++++++++++
> > >  kernel/sys.c                  |   19 ++-
> > >  6 files changed, 314 insertions(+), 7 deletions(-)
> > >  create mode 100644 kernel/cgroup_timer_slack.c
> > > 
> > > 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/include/linux/init_task.h b/include/linux/init_task.h
> > > index caa151f..48eca8f 100644
> > > --- a/include/linux/init_task.h
> > > +++ b/include/linux/init_task.h
> > > @@ -124,6 +124,8 @@ extern struct cred init_cred;
> > >  # define INIT_PERF_EVENTS(tsk)
> > >  #endif
> > > 
> > > +#define TIMER_SLACK_NS_DEFAULT 50000
> > > +
> > >  /*
> > >   *  INIT_TASK is used to set up the first task table, touch at
> > >   * your own risk!. Base=0, limit=0x1fffff (=2MB)
> > > @@ -177,7 +179,7 @@ extern struct cred init_cred;
> > >  	.cpu_timers	= INIT_CPU_TIMERS(tsk.cpu_timers),		\
> > >  	.fs_excl	= ATOMIC_INIT(0),				\
> > >  	.pi_lock	= __RAW_SPIN_LOCK_UNLOCKED(tsk.pi_lock),	\
> > > -	.timer_slack_ns = 50000, /* 50 usec default slack */		\
> > > +	.timer_slack_ns = TIMER_SLACK_NS_DEFAULT,			\
> > >  	.pids = {							\
> > >  		[PIDTYPE_PID]  = INIT_PID_LINK(PIDTYPE_PID),		\
> > >  		[PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID),		\
> > > diff --git a/init/Kconfig b/init/Kconfig
> > > index be788c0..6cf465f 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 subsystem"
> > > +	help
> > > +	  Provides a way of tasks grouping by timer slack value.
> > > +	  Introduces per cgroup timer slack value which will override
> > > +	  the default timer slack value once a task is attached to a
> > > +	  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 353d3fe..0b60239 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..609e1f1
> > > --- /dev/null
> > > +++ b/kernel/cgroup_timer_slack.c
> > > @@ -0,0 +1,281 @@
> > > +/*
> > > + * 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,
> > > +};
> > > +
> > > +extern int (*timer_slack_check)(struct task_struct *task,
> > > +		unsigned long slack_ns);
> > > +
> > > +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 task_struct *task,
> > > +		unsigned long slack_ns)
> > > +{
> > > +	struct cgroup_subsys_state *css;
> > > +	struct timer_slack_cgroup *tslack_cgroup;
> > > +
> > > +	/* XXX: lockdep false positive? */
> > > +	rcu_read_lock();
> > > +	css = task_subsys_state(task, timer_slack_subsys.subsys_id);
> > > +	tslack_cgroup = container_of(css, struct timer_slack_cgroup, css);
> > 
> > Shouldn't the rcu_read_unlock() be after the check of is_timer_slack_allowed()?
> 
> I'm not sure if this rcu_read_lock() is needed. See freezer_fork().
> 
> > > +	rcu_read_unlock();
> > > +
> > > +	if (!is_timer_slack_allowed(tslack_cgroup, slack_ns))
> > > +		return -EPERM;
> > > +	return 0;
> > > +}
> > > +
> > > +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);
> > 
> > OK, I've got questions, are the following possible
> > 
> > 1. Assign a task to a cgroup based on timer slack, it is accepted
> > based on min and max values
> 
> Hm.. Currently, there is no such functionality. Do we need it? What's use
> case?
> 
> > 2. We update the slack
> > 
> > Can't this be bad for some tasks, is there a way for a task to prevent
> > the max slack from being updated?
> 
> If a non-RT task can't tolerate not being on time it's totally broken.

Yes, I agree, except that the slack might be overwritten after the
application set an acceptable slack.

> RT-tasks are not affected by timer slack.
> 
> And we believe that user knows what he does.
> 
> > 2. Can there be an overlap in the ranges?
> 
> What overlap do you mean?
> There is only one rule: parent's range should be wider then child's.

Between the children, can we have something like

        10-200
        /    \
       /      \
      V        V
   10-110    100-200

-- 
	Three Cheers,
	Balbir

Re: [PATCH, v5 2/2] cgroups: introduce timer slack subsystem

[Kirill A. Shutemov]

On Mon, Feb 07, 2011 at 05:44:30PM +0530, Balbir Singh wrote:
> * Kirill A. Shutemov <kirill@shutemov.name> [2011-02-07 12:57:30]:
> 
> > On Mon, Feb 07, 2011 at 03:36:24PM +0530, Balbir Singh wrote:
> > > 2. Can there be an overlap in the ranges?
> > 
> > What overlap do you mean?
> > There is only one rule: parent's range should be wider then child's.
> 
> Between the children, can we have something like
> 
>         10-200
>         /    \
>        /      \
>       V        V
>    10-110    100-200

Yes, sure.

-- 
 Kirill A. Shutemov