sched: disable forced preemption by default

Implement feature bit to disable forced preemption. This way
it can be checked whether a workload is overscheduling or not.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 16 insertions, 12 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index b7dff36c7c8c..0bd8f2c0fb40 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -444,13 +444,15 @@ enum {
         SCHED_FEAT_START_DEBIT          = 2,
         SCHED_FEAT_TREE_AVG             = 4,
         SCHED_FEAT_APPROX_AVG           = 8,
+        SCHED_FEAT_WAKEUP_PREEMPT       = 16,
 };
 
 const_debug unsigned int sysctl_sched_features =
                 SCHED_FEAT_NEW_FAIR_SLEEPERS    *1 |
                 SCHED_FEAT_START_DEBIT          *1 |
                 SCHED_FEAT_TREE_AVG             *0 |
-                SCHED_FEAT_APPROX_AVG           *0;
+                SCHED_FEAT_APPROX_AVG           *0 |
+                SCHED_FEAT_WAKEUP_PREEMPT       *1;
 
 #define sched_feat(x) (sysctl_sched_features & SCHED_FEAT_##x)
 
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 3ac096e74faf..3843ec71aad5 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -626,7 +626,7 @@ static void entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
          */
         update_curr(cfs_rq);
 
-        if (cfs_rq->nr_running > 1)
+        if (cfs_rq->nr_running > 1 || !sched_feat(WAKEUP_PREEMPT))
                 check_preempt_tick(cfs_rq, curr);
 }
 
@@ -828,18 +828,20 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
                 return;
         }
 
-        while (!is_same_group(se, pse)) {
-                se = parent_entity(se);
-                pse = parent_entity(pse);
-        }
+        if (sched_feat(WAKEUP_PREEMPT)) {
+                while (!is_same_group(se, pse)) {
+                        se = parent_entity(se);
+                        pse = parent_entity(pse);
+                }
 
-        delta = se->vruntime - pse->vruntime;
-        gran = sysctl_sched_wakeup_granularity;
-        if (unlikely(se->load.weight != NICE_0_LOAD))
-                gran = calc_delta_fair(gran, &se->load);
+                delta = se->vruntime - pse->vruntime;
+                gran = sysctl_sched_wakeup_granularity;
+                if (unlikely(se->load.weight != NICE_0_LOAD))
+                        gran = calc_delta_fair(gran, &se->load);
 
-        if (delta > gran)
-                resched_task(curr);
+                if (delta > gran)
+                        resched_task(curr);
+        }
 }
 
 static struct task_struct *pick_next_task_fair(struct rq *rq)