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>

1 files changed, 43 insertions, 0 deletions

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()