Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

CFS Bandwidth Control

=====================

[ This document only discusses CPU bandwidth control for SCHED_NORMAL.

  The SCHED_RT case is covered in Documentation/scheduler/sched-rt-group.txt ]

CFS bandwidth control is a CONFIG_FAIR_GROUP_SCHED extension which allows the

specification of the maximum CPU bandwidth available to a group or hierarchy.

The bandwidth allowed for a group is specified using a quota and period. Within

each given "period" (microseconds), a group is allowed to consume only up to

"quota" microseconds of CPU time.  When the CPU bandwidth consumption of a

group exceeds this limit (for that period), the tasks belonging to its

hierarchy will be throttled and are not allowed to run again until the next

period.

A group's unused runtime is globally tracked, being refreshed with quota units

above at each period boundary.  As threads consume this bandwidth it is

transferred to cpu-local "silos" on a demand basis.  The amount transferred

within each of these updates is tunable and described as the "slice".

Management

----------

Quota and period are managed within the cpu subsystem via cgroupfs.

cpu.cfs_quota_us: the total available run-time within a period (in microseconds)

cpu.cfs_period_us: the length of a period (in microseconds)

cpu.stat: exports throttling statistics [explained further below]

The default values are:

	cpu.cfs_period_us=100ms

	cpu.cfs_quota=-1

A value of -1 for cpu.cfs_quota_us indicates that the group does not have any

bandwidth restriction in place, such a group is described as an unconstrained

bandwidth group.  This represents the traditional work-conserving behavior for

CFS.

Writing any (valid) positive value(s) will enact the specified bandwidth limit.

The minimum quota allowed for the quota or period is 1ms.  There is also an

upper bound on the period length of 1s.  Additional restrictions exist when

bandwidth limits are used in a hierarchical fashion, these are explained in

more detail below.

Writing any negative value to cpu.cfs_quota_us will remove the bandwidth limit

and return the group to an unconstrained state once more.

Any updates to a group's bandwidth specification will result in it becoming

unthrottled if it is in a constrained state.

System wide settings

--------------------

For efficiency run-time is transferred between the global pool and CPU local

"silos" in a batch fashion.  This greatly reduces global accounting pressure

on large systems.  The amount transferred each time such an update is required

is described as the "slice".

This is tunable via procfs:

	/proc/sys/kernel/sched_cfs_bandwidth_slice_us (default=5ms)

Larger slice values will reduce transfer overheads, while smaller values allow

for more fine-grained consumption.

Statistics

----------

A group's bandwidth statistics are exported via 3 fields in cpu.stat.

cpu.stat:

- nr_periods: Number of enforcement intervals that have elapsed.

- nr_throttled: Number of times the group has been throttled/limited.

- throttled_time: The total time duration (in nanoseconds) for which entities

  of the group have been throttled.

This interface is read-only.

Hierarchical considerations

---------------------------

The interface enforces that an individual entity's bandwidth is always

attainable, that is: max(c_i) <= C. However, over-subscription in the

aggregate case is explicitly allowed to enable work-conserving semantics

within a hierarchy.

  e.g. \Sum (c_i) may exceed C

[ Where C is the parent's bandwidth, and c_i its children ]

There are two ways in which a group may become throttled:

	a. it fully consumes its own quota within a period

	b. a parent's quota is fully consumed within its period

In case b) above, even though the child may have runtime remaining it will not

be allowed to until the parent's runtime is refreshed.

Examples

--------

1. Limit a group to 1 CPU worth of runtime.

	If period is 250ms and quota is also 250ms, the group will get

	1 CPU worth of runtime every 250ms.

	# echo 250000 > cpu.cfs_quota_us /* quota = 250ms */

	# echo 250000 > cpu.cfs_period_us /* period = 250ms */

2. Limit a group to 2 CPUs worth of runtime on a multi-CPU machine.

	With 500ms period and 1000ms quota, the group can get 2 CPUs worth of

	runtime every 500ms.

	# echo 1000000 > cpu.cfs_quota_us /* quota = 1000ms */

	# echo 500000 > cpu.cfs_period_us /* period = 500ms */

	The larger period here allows for increased burst capacity.

3. Limit a group to 20% of 1 CPU.

	With 50ms period, 10ms quota will be equivalent to 20% of 1 CPU.

	# echo 10000 > cpu.cfs_quota_us /* quota = 10ms */

	# echo 50000 > cpu.cfs_period_us /* period = 50ms */

	By using a small period here we are ensuring a consistent latency

	response at the expense of burst capacity.

	depends on ACPI_APEI && X86

	select ACPI_HED

	select IRQ_WORK

	select LLIST

	select GENERIC_ALLOCATOR

	help

	  Generic Hardware Error Source provides a way to report

#ifndef _LINUX_IRQ_WORK_H

#define _LINUX_IRQ_WORK_H

#include <linux/llist.h>

struct irq_work {

	struct irq_work *next;

	unsigned long flags;

	struct llist_node llnode;

	void (*func)(struct irq_work *);

};

static inline

void init_irq_work(struct irq_work *entry, void (*func)(struct irq_work *))

void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *))

{

	entry->next = NULL;

	entry->func = func;

	work->flags = 0;

	work->func = func;

}

bool irq_work_queue(struct irq_work *entry);

bool irq_work_queue(struct irq_work *work);

void irq_work_run(void);

void irq_work_sync(struct irq_work *entry);

void irq_work_sync(struct irq_work *work);

#endif /* _LINUX_IRQ_WORK_H */

 *

 * The basic atomic operation of this list is cmpxchg on long.  On

 * architectures that don't have NMI-safe cmpxchg implementation, the

 * list can NOT be used in NMI handler.  So code uses the list in NMI

 * handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.

 * list can NOT be used in NMI handlers.  So code that uses the list in

 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.

 *

 * Copyright 2010,2011 Intel Corp.

 *   Author: Huang Ying <ying.huang@intel.com>

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License version

 * 2 as published by the Free Software Foundation;

 *

 * 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.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

#include <linux/kernel.h>

#include <asm/system.h>

#include <asm/processor.h>

struct llist_head {

	struct llist_node *first;

};

 * test whether the list is empty without deleting something from the

 * list.

 */

static inline int llist_empty(const struct llist_head *head)

static inline bool llist_empty(const struct llist_head *head)

{

	return ACCESS_ONCE(head->first) == NULL;

}

void llist_add(struct llist_node *new, struct llist_head *head);

void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,

static inline struct llist_node *llist_next(struct llist_node *node)

{

	return node->next;

}

/**

 * llist_add - add a new entry

 * @new:	new entry to be added

 * @head:	the head for your lock-less list

 *

 * Return whether list is empty before adding.

 */

static inline bool llist_add(struct llist_node *new, struct llist_head *head)

{

	struct llist_node *entry, *old_entry;

	entry = head->first;

	for (;;) {

		old_entry = entry;

		new->next = entry;

		entry = cmpxchg(&head->first, old_entry, new);

		if (entry == old_entry)

			break;

	}

	return old_entry == NULL;

}

/**

 * llist_del_all - delete all entries from lock-less list

 * @head:	the head of lock-less list to delete all entries

 *

 * If list is empty, return NULL, otherwise, delete all entries and

 * return the pointer to the first entry.  The order of entries

 * deleted is from the newest to the oldest added one.

 */

static inline struct llist_node *llist_del_all(struct llist_head *head)

{

	return xchg(&head->first, NULL);

}

extern bool llist_add_batch(struct llist_node *new_first,

			    struct llist_node *new_last,

			    struct llist_head *head);

struct llist_node *llist_del_first(struct llist_head *head);

struct llist_node *llist_del_all(struct llist_head *head);

extern struct llist_node *llist_del_first(struct llist_head *head);

#endif /* LLIST_H */

#include <linux/task_io_accounting.h>

#include <linux/latencytop.h>

#include <linux/cred.h>

#include <linux/llist.h>

#include <asm/processor.h>

	unsigned int ptrace;

#ifdef CONFIG_SMP

	struct task_struct *wake_entry;

	struct llist_node wake_entry;

	int on_cpu;

#endif

	int on_rq;

static inline void sched_autogroup_exit(struct signal_struct *sig) { }

#endif

#ifdef CONFIG_CFS_BANDWIDTH

extern unsigned int sysctl_sched_cfs_bandwidth_slice;

#endif

#ifdef CONFIG_RT_MUTEXES

extern int rt_mutex_getprio(struct task_struct *p);

extern void rt_mutex_setprio(struct task_struct *p, int prio);