[PATCH] sched: add new SCHED_BATCH policy

Add a new SCHED_BATCH (3) scheduling policy: such tasks are presumed
CPU-intensive, and will acquire a constant +5 priority level penalty.  Such
policy is nice for workloads that are non-interactive, but which do not
want to give up their nice levels.  The policy is also useful for workloads
that want a deterministic scheduling policy without interactivity causing
extra preemptions (between that workload's tasks).

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 40 insertions, 19 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a72e17135421..2df1a1a2fee5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -160,6 +160,7 @@ extern unsigned long nr_iowait(void);
 #define SCHED_NORMAL            0
 #define SCHED_FIFO              1
 #define SCHED_RR                2
+#define SCHED_BATCH             3
 
 struct sched_param {
         int sched_priority;
@@ -470,9 +471,9 @@ struct signal_struct {
 
 /*
  * Priority of a process goes from 0..MAX_PRIO-1, valid RT
- * priority is 0..MAX_RT_PRIO-1, and SCHED_NORMAL tasks are
- * in the range MAX_RT_PRIO..MAX_PRIO-1. Priority values
- * are inverted: lower p->prio value means higher priority.
+ * priority is 0..MAX_RT_PRIO-1, and SCHED_NORMAL/SCHED_BATCH
+ * tasks are in the range MAX_RT_PRIO..MAX_PRIO-1. Priority
+ * values are inverted: lower p->prio value means higher priority.
  *
  * The MAX_USER_RT_PRIO value allows the actual maximum
  * RT priority to be separate from the value exported to
diff --git a/kernel/exit.c b/kernel/exit.c
index f8e609ff1893..7fb541cb8d69 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -244,7 +244,9 @@ static inline void reparent_to_init(void)
         /* Set the exit signal to SIGCHLD so we signal init on exit */
         current->exit_signal = SIGCHLD;
 
-        if ((current->policy == SCHED_NORMAL) && (task_nice(current) < 0))
+        if ((current->policy == SCHED_NORMAL ||
+                        current->policy == SCHED_BATCH)
+                                && (task_nice(current) < 0))
                 set_user_nice(current, 0);
         /* cpus_allowed? */
         /* rt_priority? */
diff --git a/kernel/sched.c b/kernel/sched.c
index c9dec2aa1976..e1dc903d5a75 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -748,10 +748,14 @@ static int recalc_task_prio(task_t *p, unsigned long long now)
         unsigned long long __sleep_time = now - p->timestamp;
         unsigned long sleep_time;
 
-        if (__sleep_time > NS_MAX_SLEEP_AVG)
-                sleep_time = NS_MAX_SLEEP_AVG;
-        else
-                sleep_time = (unsigned long)__sleep_time;
+        if (unlikely(p->policy == SCHED_BATCH))
+                sleep_time = 0;
+        else {
+                if (__sleep_time > NS_MAX_SLEEP_AVG)
+                        sleep_time = NS_MAX_SLEEP_AVG;
+                else
+                        sleep_time = (unsigned long)__sleep_time;
+        }
 
         if (likely(sleep_time > 0)) {
                 /*
@@ -3560,7 +3564,7 @@ void set_user_nice(task_t *p, long nice)
          * The RT priorities are set via sched_setscheduler(), but we still
          * allow the 'normal' nice value to be set - but as expected
          * it wont have any effect on scheduling until the task is
-         * not SCHED_NORMAL:
+         * not SCHED_NORMAL/SCHED_BATCH:
          */
         if (rt_task(p)) {
                 p->static_prio = NICE_TO_PRIO(nice);
@@ -3706,10 +3710,16 @@ static void __setscheduler(struct task_struct *p, int policy, int prio)
         BUG_ON(p->array);
         p->policy = policy;
         p->rt_priority = prio;
-        if (policy != SCHED_NORMAL)
+        if (policy != SCHED_NORMAL && policy != SCHED_BATCH) {
                 p->prio = MAX_RT_PRIO-1 - p->rt_priority;
-        else
+        } else {
                 p->prio = p->static_prio;
+                /*
+                 * SCHED_BATCH tasks are treated as perpetual CPU hogs:
+                 */
+                if (policy == SCHED_BATCH)
+                        p->sleep_avg = 0;
+        }
 }
 
 /**
@@ -3733,29 +3743,35 @@ recheck:
         if (policy < 0)
                 policy = oldpolicy = p->policy;
         else if (policy != SCHED_FIFO && policy != SCHED_RR &&
-                                policy != SCHED_NORMAL)
-                        return -EINVAL;
+                        policy != SCHED_NORMAL && policy != SCHED_BATCH)
+                return -EINVAL;
         /*
          * Valid priorities for SCHED_FIFO and SCHED_RR are
-         * 1..MAX_USER_RT_PRIO-1, valid priority for SCHED_NORMAL is 0.
+         * 1..MAX_USER_RT_PRIO-1, valid priority for SCHED_NORMAL and
+         * SCHED_BATCH is 0.
          */
         if (param->sched_priority < 0 ||
             (p->mm && param->sched_priority > MAX_USER_RT_PRIO-1) ||
             (!p->mm && param->sched_priority > MAX_RT_PRIO-1))
                 return -EINVAL;
-        if ((policy == SCHED_NORMAL) != (param->sched_priority == 0))
+        if ((policy == SCHED_NORMAL || policy == SCHED_BATCH)
+                                        != (param->sched_priority == 0))
                 return -EINVAL;
 
         /*
          * Allow unprivileged RT tasks to decrease priority:
          */
         if (!capable(CAP_SYS_NICE)) {
-                /* can't change policy */
-                if (policy != p->policy &&
-                        !p->signal->rlim[RLIMIT_RTPRIO].rlim_cur)
+                /*
+                 * can't change policy, except between SCHED_NORMAL
+                 * and SCHED_BATCH:
+                 */
+                if (((policy != SCHED_NORMAL && p->policy != SCHED_BATCH) &&
+                        (policy != SCHED_BATCH && p->policy != SCHED_NORMAL)) &&
+                                !p->signal->rlim[RLIMIT_RTPRIO].rlim_cur)
                         return -EPERM;
                 /* can't increase priority */
-                if (policy != SCHED_NORMAL &&
+                if ((policy != SCHED_NORMAL && policy != SCHED_BATCH) &&
                     param->sched_priority > p->rt_priority &&
                     param->sched_priority >
                                 p->signal->rlim[RLIMIT_RTPRIO].rlim_cur)
@@ -4233,6 +4249,7 @@ asmlinkage long sys_sched_get_priority_max(int policy)
                 ret = MAX_USER_RT_PRIO-1;
                 break;
         case SCHED_NORMAL:
+        case SCHED_BATCH:
                 ret = 0;
                 break;
         }
@@ -4256,6 +4273,7 @@ asmlinkage long sys_sched_get_priority_min(int policy)
                 ret = 1;
                 break;
         case SCHED_NORMAL:
+        case SCHED_BATCH:
                 ret = 0;
         }
         return ret;