sched: Add 'autogroup' scheduling feature: automated per session task groups

A recurring complaint from CFS users is that parallel kbuild has
a negative impact on desktop interactivity.  This patch
implements an idea from Linus, to automatically create task
groups.  Currently, only per session autogroups are implemented,
but the patch leaves the way open for enhancement.

Implementation: each task's signal struct contains an inherited
pointer to a refcounted autogroup struct containing a task group
pointer, the default for all tasks pointing to the
init_task_group.  When a task calls setsid(), a new task group
is created, the process is moved into the new task group, and a
reference to the preveious task group is dropped.  Child
processes inherit this task group thereafter, and increase it's
refcount.  When the last thread of a process exits, the
process's reference is dropped, such that when the last process
referencing an autogroup exits, the autogroup is destroyed.

At runqueue selection time, IFF a task has no cgroup assignment,
its current autogroup is used.

Autogroup bandwidth is controllable via setting it's nice level
through the proc filesystem:

  cat /proc/<pid>/autogroup

Displays the task's group and the group's nice level.

  echo <nice level> > /proc/<pid>/autogroup

Sets the task group's shares to the weight of nice <level> task.
Setting nice level is rate limited for !admin users due to the
abuse risk of task group locking.

The feature is enabled from boot by default if
CONFIG_SCHED_AUTOGROUP=y is selected, but can be disabled via
the boot option noautogroup, and can also be turned on/off on
the fly via:

  echo [01] > /proc/sys/kernel/sched_autogroup_enabled

... which will automatically move tasks to/from the root task group.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Paul Turner <pjt@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
[ Removed the task_group_path() debug code, and fixed !EVENTFD build failure. ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <1290281700.28711.9.camel@maggy.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 45 deletions

diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index e95b77414a99..1dfae3d014b5 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -54,8 +54,7 @@ static unsigned long nsec_low(unsigned long long nsec)
 #define SPLIT_NS(x) nsec_high(x), nsec_low(x)
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-static void print_cfs_group_stats(struct seq_file *m, int cpu,
-                struct task_group *tg)
+static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group *tg)
 {
         struct sched_entity *se = tg->se[cpu];
         if (!se)
@@ -110,16 +109,6 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
                 0LL, 0LL, 0LL, 0L, 0LL, 0L, 0LL, 0L);
 #endif
 
-#ifdef CONFIG_CGROUP_SCHED
-        {
-                char path[64];
-
-                rcu_read_lock();
-                cgroup_path(task_group(p)->css.cgroup, path, sizeof(path));
-                rcu_read_unlock();
-                SEQ_printf(m, " %s", path);
-        }
-#endif
         SEQ_printf(m, "\n");
 }
 
@@ -147,19 +136,6 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
         read_unlock_irqrestore(&tasklist_lock, flags);
 }
 
-#if defined(CONFIG_CGROUP_SCHED) && \
-        (defined(CONFIG_FAIR_GROUP_SCHED) || defined(CONFIG_RT_GROUP_SCHED))
-static void task_group_path(struct task_group *tg, char *buf, int buflen)
-{
-        /* may be NULL if the underlying cgroup isn't fully-created yet */
-        if (!tg->css.cgroup) {
-                buf[0] = '\0';
-                return;
-        }
-        cgroup_path(tg->css.cgroup, buf, buflen);
-}
-#endif
-
 void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 {
         s64 MIN_vruntime = -1, min_vruntime, max_vruntime = -1,
@@ -168,16 +144,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
         struct sched_entity *last;
         unsigned long flags;
 
-#if defined(CONFIG_CGROUP_SCHED) && defined(CONFIG_FAIR_GROUP_SCHED)
-        char path[128];
-        struct task_group *tg = cfs_rq->tg;
-
-        task_group_path(tg, path, sizeof(path));
-
-        SEQ_printf(m, "\ncfs_rq[%d]:%s\n", cpu, path);
-#else
         SEQ_printf(m, "\ncfs_rq[%d]:\n", cpu);
-#endif
         SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "exec_clock",
                         SPLIT_NS(cfs_rq->exec_clock));
 
@@ -215,7 +182,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
         SEQ_printf(m, "  .%-30s: %ld\n", "load_contrib",
                         cfs_rq->load_contribution);
         SEQ_printf(m, "  .%-30s: %d\n", "load_tg",
-                        atomic_read(&tg->load_weight));
+                        atomic_read(&cfs_rq->tg->load_weight));
 #endif
 
         print_cfs_group_stats(m, cpu, cfs_rq->tg);
@@ -224,17 +191,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 
 void print_rt_rq(struct seq_file *m, int cpu, struct rt_rq *rt_rq)
 {
-#if defined(CONFIG_CGROUP_SCHED) && defined(CONFIG_RT_GROUP_SCHED)
-        char path[128];
-        struct task_group *tg = rt_rq->tg;
-
-        task_group_path(tg, path, sizeof(path));
-
-        SEQ_printf(m, "\nrt_rq[%d]:%s\n", cpu, path);
-#else
         SEQ_printf(m, "\nrt_rq[%d]:\n", cpu);
-#endif
-
 
 #define P(x) \
         SEQ_printf(m, "  .%-30s: %Ld\n", #x, (long long)(rt_rq->x))