[RFC/PATCH -v2] Add sysfs control to modify a user's cpu share

Dhaval Giani
2007-10-03T17:16:09Z

Hi Ingo,

Can you please drop commit b1add858a10cece3a68b2d8cb9e7350843700a58 (last
version of this patch) and try this instead?
---
Adds tunables in sysfs to modify a user's cpu share.

A directory is created in sysfs for each new user in the system.

/sys/kernel/uids/<uid>/cpu_share

Reading this file returns the cpu shares granted for the user.
Writing into this file modifies the cpu share for the user. Only an
administrator is allowed to modify a user's cpu share.

Ex:
# cd /sys/kernel/uids/
# cat 512/cpu_share
1024
# echo 2048 > 512/cpu_share
# cat 512/cpu_share
2048
#

Changelog since v1:
1. Added a mutex to serialize directory creation/destruction for a user in
sysfs
2. Added a spinlock in the task_group structure to serialize writes to
tg->shares.
3. Removed /proc/root_user_cpu_shares.
4. Added Documentation about the group scheduler.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>

---
Documentation/sched-design-CFS.txt | 67 ++++++++++
include/linux/sched.h | 11 +
kernel/ksysfs.c | 8 +
kernel/sched.c | 14 +-
kernel/sched_debug.c | 48 -------
kernel/user.c | 242 ++++++++++++++++++++++++++++++++-----
6 files changed, 310 insertions(+), 80 deletions(-)

Index: linux-2.6.23-rc8-sched-devel/Documentation/sched-design-CFS.txt
===================================================================
--- linux-2.6.23-rc8-sched-devel.orig/Documentation/sched-design-CFS.txt
+++ linux-2.6.23-rc8-sched-devel/Documentation/sched-design-CFS.txt
@@ -117,3 +117,70 @@ Some implementation details:
iterators of the scheduling modules are used. The balancing code got
quite a bit simpler as a result.

+
+Group scheduler extension to CFS
+================================
+
+Normally the scheduler operates on individual tasks and strives to provide
+fair CPU time to each task. Sometimes, it may be desirable to group tasks
+and provide fair CPU time to each such task group. For example, it may
+be desirable to first provide fair CPU time to each user on the system
+and then to each task belonging to a user.
+
+CONFIG_FAIR_GROUP_SCHED strives to achieve exactly that. It lets
+SCHED_NORMAL/BATCH tasks be be grouped and divides CPU time fairly among such
+groups. At present, there are two (mutually exclusive) mechanisms to group
+tasks for CPU bandwidth control purpose:
+
+ - Based on user id (CONFIG_FAIR_USER_SCHED)
+ In this option, tasks are grouped according to their user id.
+ - Based on "cgroup" pseudo filesystem (CONFIG_FAIR_CGROUP_SCHED)
+ This options lets the administrator create arbitrary groups
+ of tasks, using the "cgroup" pseudo filesystem. See
+ Documentation/cgroups.txt for more information about this
+ filesystem.
+
+Only one of these options to group tasks can be chosen and not both.
+
+Group scheduler tunables:
+
+When CONFIG_FAIR_USER_SCHED is defined, a directory is created in sysfs for
+each new user and a "cpu_share" file is added in that directory.
+
+ # cd /sys/kernel/uids
+ # cat 512/cpu_share # Display user 512's CPU share
+ 1024
+ # echo 2048 > 512/cpu_share # Modify user 512's CPU share
+ # cat 512/cpu_share # Display user 512's CPU share
+ 2048
+ #
+
+CPU bandwidth between two users are divided in the ratio of their CPU shares.
+For ex: if you would like user "root" to get twice the bandwidth of user
+"guest", then set the cpu_share for both the users such that "root"'s
+cpu_share is twice "guest"'s cpu_share
+
+
+When CONFIG_FAIR_CGROUP_SCHED is defined, a "cpu.shares" file is created
+for each group created using the pseudo filesystem. See example steps
+below to create task groups and modify their CPU share using the "cgroups"
+pseudo filesystem
+
+ # mkdir /dev/cpuctl
+ # mount -t cgroup -ocpu none /dev/cpuctl
+ # cd /dev/cpuctl
+
+ # mkdir multimedia # create "multimedia" group of tasks
+ # mkdir browser # create "browser" group of tasks
+
+ # #Configure the multimedia group to receive twice the CPU bandwidth
+ # #that of browser group
+
+ # echo 2048 > multimedia/cpu.shares
+ # echo 1024 > browser/cpu.shares
+
+ # firefox & # Launch firefox and move it to "browser" group
+ # echo <firefox_pid> > browser/tasks
+
+ # #Launch gmplayer (or your favourite movie player)
+ # echo <movie_player_pid> > multimedia/tasks
Index: linux-2.6.23-rc8-sched-devel/include/linux/sched.h
===================================================================
--- linux-2.6.23-rc8-sched-devel.orig/include/linux/sched.h
+++ linux-2.6.23-rc8-sched-devel/include/linux/sched.h
@@ -86,6 +86,7 @@ struct sched_param {
#include <linux/timer.h>
#include <linux/hrtimer.h>
#include <linux/task_io_accounting.h>
+#include <linux/kobject.h>

#include <asm/processor.h>

@@ -598,9 +599,18 @@ struct user_struct {

#ifdef CONFIG_FAIR_USER_SCHED
struct task_group *tg;
+ struct kset kset;
+ struct subsys_attribute user_attr;
+ struct work_struct work;
#endif
};

+#ifdef CONFIG_FAIR_USER_SCHED
+extern int uids_kobject_init(void);
+#else
+static inline int uids_kobject_init(void) { return 0; }
+#endif
+
extern struct user_struct *find_user(uid_t);

extern struct user_struct root_user;
@@ -1846,6 +1856,7 @@ extern struct task_group *sched_create_g
extern void sched_destroy_group(struct task_group *tg);
extern void sched_move_task(struct task_struct *tsk);
extern int sched_group_set_shares(struct task_group *tg, unsigned long shares);
+extern unsigned long sched_group_shares(struct task_group *tg);

#endif

Index: linux-2.6.23-rc8-sched-devel/kernel/ksysfs.c
===================================================================
--- linux-2.6.23-rc8-sched-devel.orig/kernel/ksysfs.c
+++ linux-2.6.23-rc8-sched-devel/kernel/ksysfs.c
@@ -14,6 +14,7 @@
#include <linux/module.h>
#include <linux/init.h>
#include <linux/kexec.h>
+#include <linux/sched.h>

#define KERNEL_ATTR_RO(_name) \
static struct subsys_attribute _name##_attr = __ATTR_RO(_name)
@@ -116,6 +117,13 @@ static int __init ksysfs_init(void)
&notes_attr);
}

+ /*
+ * Create "/sys/kernel/uids" directory and corresponding root user's
+ * directory under it.
+ */
+ if (!error)
+ error = uids_kobject_init();
+
return error;
}

Index: linux-2.6.23-rc8-sched-devel/kernel/sched.c
===================================================================
--- linux-2.6.23-rc8-sched-devel.orig/kernel/sched.c
+++ linux-2.6.23-rc8-sched-devel/kernel/sched.c
@@ -161,6 +161,8 @@ struct task_group {
/* runqueue "owned" by this group on each cpu */
struct cfs_rq **cfs_rq;
unsigned long shares;
+ /* spinlock to serialize modification to shares */
+ spinlock_t lock;
};

/* Default task group's sched entity on each cpu */
@@ -6552,6 +6554,7 @@ void __init sched_init(void)
se->parent = NULL;
}
init_task_group.shares = init_task_group_load;
+ spin_lock_init(&init_task_group.lock);
#endif

for (j = 0; j < CPU_LOAD_IDX_MAX; j++)
@@ -6796,6 +6799,7 @@ struct task_group *sched_create_group(vo
}

tg->shares = NICE_0_LOAD;
+ spin_lock_init(&tg->lock);

return tg;

@@ -6916,8 +6920,9 @@ int sched_group_set_shares(struct task_g
{
int i;

+ spin_lock(&tg->lock);
if (tg->shares == shares)
- return 0;
+ goto done;

/* return -EINVAL if the new value is not sane */

@@ -6925,7 +6930,14 @@ int sched_group_set_shares(struct task_g
for_each_possible_cpu(i)
set_se_shares(tg->se[i], shares);

+done:
+ spin_unlock(&tg->lock);
return 0;
}

+unsigned long sched_group_shares(struct task_group *tg)
+{
+ return tg->shares;
+}
+
#endif /* CONFIG_FAIR_GROUP_SCHED */
Index: linux-2.6.23-rc8-sched-devel/kernel/sched_debug.c
===================================================================
--- linux-2.6.23-rc8-sched-devel.orig/kernel/sched_debug.c
+++ linux-2.6.23-rc8-sched-devel/kernel/sched_debug.c
@@ -231,45 +231,6 @@ static void sysrq_sched_debug_show(void)
sched_debug_show(NULL, NULL);
}

-#ifdef CONFIG_FAIR_USER_SCHED
-
-static DEFINE_MUTEX(root_user_share_mutex);
-
-static int
-root_user_share_read_proc(char *page, char **start, off_t off, int count,
- int *eof, void *data)
-{
- return sprintf(page, "%d\n", init_task_group_load);
-}
-
-static int
-root_user_share_write_proc(struct file *file, const char __user *buffer,
- unsigned long count, void *data)
-{
- unsigned long shares;
- char kbuf[sizeof(unsigned long)+1];
- int rc = 0;
-
- if (copy_from_user(kbuf, buffer, sizeof(kbuf)))
- return -EFAULT;
-
- shares = simple_strtoul(kbuf, NULL, 0);
-
- if (!shares)
- shares = NICE_0_LOAD;
-
- mutex_lock(&root_user_share_mutex);
-
- init_task_group_load = shares;
- rc = sched_group_set_shares(&init_task_group, shares);
-
- mutex_unlock(&root_user_share_mutex);
-
- return (rc < 0 ? rc : count);
-}
-
-#endif /* CONFIG_FAIR_USER_SCHED */
-
static int sched_debug_open(struct inode *inode, struct file *filp)
{
return single_open(filp, sched_debug_show, NULL);
@@ -292,15 +253,6 @@ static int __init init_sched_debug_procf

pe->proc_fops = &sched_debug_fops;

-#ifdef CONFIG_FAIR_USER_SCHED
- pe = create_proc_entry("root_user_cpu_share", 0644, NULL);
- if (!pe)
- return -ENOMEM;
-
- pe->read_proc = root_user_share_read_proc;
- pe->write_proc = root_user_share_write_proc;
-#endif
-
return 0;
}

Index: linux-2.6.23-rc8-sched-devel/kernel/user.c
===================================================================
--- linux-2.6.23-rc8-sched-devel.orig/kernel/user.c
+++ linux-2.6.23-rc8-sched-devel/kernel/user.c
@@ -55,7 +55,41 @@ struct user_struct root_user = {
#endif
};

+/*
+ * These routines must be called with the uidhash spinlock held!
+ */
+static inline void uid_hash_insert(struct user_struct *up,
+ struct hlist_head *hashent)
+{
+ hlist_add_head(&up->uidhash_node, hashent);
+}
+
+static inline void uid_hash_remove(struct user_struct *up)
+{
+ hlist_del_init(&up->uidhash_node);
+}
+
+static inline struct user_struct *uid_hash_find(uid_t uid,
+ struct hlist_head *hashent)
+{
+ struct user_struct *user;
+ struct hlist_node *h;
+
+ hlist_for_each_entry(user, h, hashent, uidhash_node) {
+ if (user->uid == uid) {
+ atomic_inc(&user->__count);
+ return user;
+ }
+ }
+
+ return NULL;
+}
+
#ifdef CONFIG_FAIR_USER_SCHED
+
+static struct kobject uids_kobject; /* represents /sys/kernel/uids directory */
+static DEFINE_MUTEX(uids_mutex);
+
static void sched_destroy_user(struct user_struct *up)
{
sched_destroy_group(up->tg);
@@ -77,42 +111,173 @@ static void sched_switch_user(struct tas
sched_move_task(p);
}

-#else /* CONFIG_FAIR_USER_SCHED */
+static inline void uids_mutex_lock(void)
+{
+ mutex_lock(&uids_mutex);
+}

-static void sched_destroy_user(struct user_struct *up) { }
-static int sched_create_user(struct user_struct *up) { return 0; }
-static void sched_switch_user(struct task_struct *p) { }
+static inline void uids_mutex_unlock(void)
+{
+ mutex_unlock(&uids_mutex);
+}

-#endif /* CONFIG_FAIR_USER_SCHED */
+/* return cpu shares held by the user */
+ssize_t cpu_shares_show(struct kset *kset, char *buffer)
+{
+ struct user_struct *up = container_of(kset, struct user_struct, kset);

-/*
- * These routines must be called with the uidhash spinlock held!
- */
-static inline void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
+ return sprintf(buffer, "%lu\n", sched_group_shares(up->tg));
+}
+
+/* modify cpu shares held by the user */
+ssize_t cpu_shares_store(struct kset *kset, const char *buffer, size_t size)
{
- hlist_add_head(&up->uidhash_node, hashent);
+ struct user_struct *up = container_of(kset, struct user_struct, kset);
+ unsigned long shares;
+ int rc;
+
+ sscanf(buffer, "%lu", &shares);
+
+ rc = sched_group_set_shares(up->tg, shares);
+
+ return (rc ? rc : size);
}

-static inline void uid_hash_remove(struct user_struct *up)
+static void user_attr_init(struct subsys_attribute *sa, char *name, int mode)
{
- hlist_del_init(&up->uidhash_node);
+ sa->attr.name = name;
+ sa->attr.mode = mode;
+ sa->show = cpu_shares_show;
+ sa->store = cpu_shares_store;
}

-static inline struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
+/* Create "/sys/kernel/uids/<uid>" directory and
+ * "/sys/kernel/uids/<uid>/cpu_share" file for this user.
+ */
+static int user_kobject_create(struct user_struct *up)
{
- struct user_struct *user;
- struct hlist_node *h;
+ struct kset *kset = &up->kset;
+ struct kobject *kobj = &kset->kobj;
+ int error;
+
+ memset(kset, 0, sizeof(struct kset));
+ kobj->parent = &uids_kobject; /* create under /sys/kernel/uids dir */
+ kobject_set_name(kobj, "%d", up->uid);
+ kset_init(kset);
+ user_attr_init(&up->user_attr, "cpu_share", 0644);
+
+ error = kobject_add(kobj);
+ if (error)
+ goto done;
+
+ error = sysfs_create_file(kobj, &up->user_attr.attr);
+ if (error)
+ kobject_del(kobj);
+
+done:
+ return error;
+}
+
+/* create these in sysfs filesystem:
+ * "/sys/kernel/uids" directory
+ * "/sys/kernel/uids/0" directory (for root user)
+ * "/sys/kernel/uids/0/cpu_share" file (for root user)
+ */
+int __init uids_kobject_init(void)
+{
+ int error;

- hlist_for_each_entry(user, h, hashent, uidhash_node) {
- if(user->uid == uid) {
- atomic_inc(&user->__count);
- return user;
- }
+ /* create under /sys/kernel dir */
+ uids_kobject.parent = &kernel_subsys.kobj;
+ kobject_set_name(&uids_kobject, "uids");
+ kobject_init(&uids_kobject);
+
+ error = kobject_add(&uids_kobject);
+ if (!error)
+ error = user_kobject_create(&root_user);
+
+ return error;
+}
+
+/* work function to remove sysfs directory for a user and free up
+ * corresponding structures.
+ */
+static void remove_user_sysfs_dir(struct work_struct *w)
+{
+ struct user_struct *up = container_of(w, struct user_struct, work);
+ struct kobject *kobj = &up->kset.kobj;
+ unsigned long flags;
+ int remove_user = 0;
+
+ /* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
+ * atomic.
+ */
+ uids_mutex_lock();
+
+ local_irq_save(flags);
+
+ if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
+ uid_hash_remove(up);
+ remove_user = 1;
+ spin_unlock_irqrestore(&uidhash_lock, flags);
+ } else {
+ local_irq_restore(flags);
}

- return NULL;
+ if (!remove_user)
+ goto done;
+
+ sysfs_remove_file(kobj, &up->user_attr.attr);
+ kobject_del(kobj);
+
+ sched_destroy_user(up);
+ key_put(up->uid_keyring);
+ key_put(up->session_keyring);
+ kmem_cache_free(uid_cachep, up);
+
+done:
+ uids_mutex_unlock();
+}
+
+/* IRQs are disabled and uidhash_lock is held upon function entry.
+ * IRQ state (as stored in flags) is restored and uidhash_lock released
+ * upon function exit.
+ */
+static inline void free_user(struct user_struct *up, unsigned long flags)
+{
+ /* restore back the count */
+ atomic_inc(&up->__count);
+ spin_unlock_irqrestore(&uidhash_lock, flags);
+
+ INIT_WORK(&up->work, remove_user_sysfs_dir);
+ schedule_work(&up->work);
+}
+
+#else /* CONFIG_FAIR_USER_SCHED */
+
+static void sched_destroy_user(struct user_struct *up) { }
+static int sched_create_user(struct user_struct *up) { return 0; }
+static void sched_switch_user(struct task_struct *p) { }
+static inline int user_kobject_create(struct user_struct *up) { return 0; }
+static inline void uids_mutex_lock(void) { }
+static inline void uids_mutex_unlock(void) { }
+
+/* IRQs are disabled and uidhash_lock is held upon function entry.
+ * IRQ state (as stored in flags) is restored and uidhash_lock released
+ * upon function exit.
+ */
+static inline void free_user(struct user_struct *up, unsigned long flags)
+{
+ uid_hash_remove(up);
+ spin_unlock_irqrestore(&uidhash_lock, flags);
+ sched_destroy_user(up);
+ key_put(up->uid_keyring);
+ key_put(up->session_keyring);
+ kmem_cache_free(uid_cachep, up);
}

+#endif /* CONFIG_FAIR_USER_SCHED */
+
/*
* Locate the user_struct for the passed UID. If found, take a ref on it. The
* caller must undo that ref with free_uid().
@@ -139,16 +304,10 @@ void free_uid(struct user_struct *up)
return;

local_irq_save(flags);
- if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
- uid_hash_remove(up);
- spin_unlock_irqrestore(&uidhash_lock, flags);
- sched_destroy_user(up);
- key_put(up->uid_keyring);
- key_put(up->session_keyring);
- kmem_cache_free(uid_cachep, up);
- } else {
+ if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
+ free_user(up, flags);
+ else
local_irq_restore(flags);
- }
}

struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
@@ -156,6 +315,11 @@ struct user_struct * alloc_uid(struct us
struct hlist_head *hashent = uidhashentry(ns, uid);
struct user_struct *up;

+ /* Make uid_hash_find() + user_kobject_create() + uid_hash_insert()
+ * atomic.
+ */
+ uids_mutex_lock();
+
spin_lock_irq(&uidhash_lock);
up = uid_hash_find(uid, hashent);
spin_unlock_irq(&uidhash_lock);
@@ -191,6 +355,15 @@ struct user_struct * alloc_uid(struct us
return NULL;
}

+ if (user_kobject_create(new)) {
+ sched_destroy_user(new);
+ key_put(new->uid_keyring);
+ key_put(new->session_keyring);
+ kmem_cache_free(uid_cachep, new);
+ uids_mutex_unlock();
+ return NULL;
+ }
+
/*
* Before adding this, check whether we raced
* on adding the same user already..
@@ -198,7 +371,11 @@ struct user_struct * alloc_uid(struct us
spin_lock_irq(&uidhash_lock);
up = uid_hash_find(uid, hashent);
if (up) {
- sched_destroy_user(new);
+ /* This case is not possible when CONFIG_FAIR_USER_SCHED
+ * is defined, since we serialize alloc_uid() using
+ * uids_mutex. Hence no need to call
+ * sched_destroy_user() or remove_user_sysfs_dir().
+ */
key_put(new->uid_keyring);
key_put(new->session_keyring);
kmem_cache_free(uid_cachep, new);
@@ -209,6 +386,9 @@ struct user_struct * alloc_uid(struct us
spin_unlock_irq(&uidhash_lock);

}
+
+ uids_mutex_unlock();
+
return up;
}

--
regards,
Dhaval