sched: add fair-user scheduler

Enable user-id based fair group scheduling. This is useful for anyone
who wants to test the group scheduler w/o having to enable
CONFIG_CGROUPS.

A separate scheduling group (i.e struct task_grp) is automatically created for 
every new user added to the system. Upon uid change for a task, it is made to 
move to the corresponding scheduling group.

A /proc tunable (/proc/root_user_share) is also provided to tune root
user's quota of cpu bandwidth.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

5 files changed, 121 insertions, 0 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 03c13b663e4b..d0cc58311b13 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -597,6 +597,10 @@ struct user_struct {
         /* Hash table maintenance information */
         struct hlist_node uidhash_node;
         uid_t uid;
+
+#ifdef CONFIG_FAIR_USER_SCHED
+        struct task_grp *tg;
+#endif
 };
 
 extern struct user_struct *find_user(uid_t);
diff --git a/init/Kconfig b/init/Kconfig
index ef90a154dd90..37711fe3c01c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -289,6 +289,19 @@ config FAIR_GROUP_SCHED
           This feature lets cpu scheduler recognize task groups and control cpu
           bandwidth allocation to such task groups.
 
+choice
+        depends on FAIR_GROUP_SCHED
+        prompt "Basis for grouping tasks"
+        default FAIR_USER_SCHED
+
+        config FAIR_USER_SCHED
+                bool "user id"
+                help
+                  This option will choose userid as the basis for grouping
+                  tasks, thus providing equal cpu bandwidth to each user.
+
+endchoice
+
 config SYSFS_DEPRECATED
         bool "Create deprecated sysfs files"
         default y
diff --git a/kernel/sched.c b/kernel/sched.c
index e10c403b1213..f33608e9e1a2 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -200,7 +200,12 @@ struct task_grp init_task_grp =  {
                                 .cfs_rq = init_cfs_rq_p,
                                  };
 
+#ifdef CONFIG_FAIR_USER_SCHED
+#define INIT_TASK_GRP_LOAD      2*NICE_0_LOAD
+#else
 #define INIT_TASK_GRP_LOAD      NICE_0_LOAD
+#endif
+
 static int init_task_grp_load = INIT_TASK_GRP_LOAD;
 
 /* return group to which a task belongs */
@@ -208,7 +213,11 @@ static inline struct task_grp *task_grp(struct task_struct *p)
 {
         struct task_grp *tg;
 
+#ifdef CONFIG_FAIR_USER_SCHED
+        tg = p->user->tg;
+#else
         tg  = &init_task_grp;
+#endif
 
         return tg;
 }
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index 3e47e870b043..57ee9d5630a8 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -212,6 +212,49 @@ 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)
+{
+        int len;
+
+        len = sprintf(page, "%d\n", init_task_grp_load);
+
+        return len;
+}
+
+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_grp_load = shares;
+        rc = sched_group_set_shares(&init_task_grp, 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);
@@ -234,6 +277,15 @@ static int __init init_sched_debug_procfs(void)
 
         pe->proc_fops = &sched_debug_fops;
 
+#ifdef CONFIG_FAIR_USER_SCHED
+        pe = create_proc_entry("root_user_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;
 }
 
diff --git a/kernel/user.c b/kernel/user.c
index 9ca2848fc356..c6387fac932d 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -50,8 +50,41 @@ struct user_struct root_user = {
         .uid_keyring    = &root_user_keyring,
         .session_keyring = &root_session_keyring,
 #endif
+#ifdef CONFIG_FAIR_USER_SCHED
+        .tg             = &init_task_grp,
+#endif
 };
 
+#ifdef CONFIG_FAIR_USER_SCHED
+static void sched_destroy_user(struct user_struct *up)
+{
+        sched_destroy_group(up->tg);
+}
+
+static int sched_create_user(struct user_struct *up)
+{
+        int rc = 0;
+
+        up->tg = sched_create_group();
+        if (IS_ERR(up->tg))
+                rc = -ENOMEM;
+
+        return rc;
+}
+
+static void sched_switch_user(struct task_struct *p)
+{
+        sched_move_task(p);
+}
+
+#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) { }
+
+#endif  /* CONFIG_FAIR_USER_SCHED */
+
 /*
  * These routines must be called with the uidhash spinlock held!
  */
@@ -109,6 +142,7 @@ void free_uid(struct user_struct *up)
         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);
@@ -150,6 +184,13 @@ struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
                         return NULL;
                 }
 
+                if (sched_create_user(new) < 0) {
+                        key_put(new->uid_keyring);
+                        key_put(new->session_keyring);
+                        kmem_cache_free(uid_cachep, new);
+                        return NULL;
+                }
+
                 /*
                  * Before adding this, check whether we raced
                  * on adding the same user already..
@@ -157,6 +198,7 @@ struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
                 spin_lock_irq(&uidhash_lock);
                 up = uid_hash_find(uid, hashent);
                 if (up) {
+                        sched_destroy_user(new);
                         key_put(new->uid_keyring);
                         key_put(new->session_keyring);
                         kmem_cache_free(uid_cachep, new);
@@ -184,6 +226,7 @@ void switch_uid(struct user_struct *new_user)
         atomic_dec(&old_user->processes);
         switch_uid_keyring(new_user);
         current->user = new_user;
+        sched_switch_user(current);
 
         /*
          * We need to synchronize with __sigqueue_alloc()