sched: wakeup preempt when small overlap

commit 15afe09bf496ae10c989e1a375a6b5da7bd3e16e upstream.

Lin Ming reported a 10% OLTP regression against 2.6.27-rc4.

The difference seems to come from different preemption agressiveness,
which affects the cache footprint of the workload and its effective
cache trashing.

Aggresively preempt a task if its avg overlap is very small, this should
avoid the task going to sleep and find it still running when we schedule
back to it - saving a wakeup.

Reported-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 20d6dd5..6d32974 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -901,7 +901,7 @@ struct sched_class {
        void (*yield_task) (struct rq *rq);
        int  (*select_task_rq)(struct task_struct *p, int sync);
 
-       void (*check_preempt_curr) (struct rq *rq, struct task_struct *p);
+       void (*check_preempt_curr) (struct rq *rq, struct task_struct *p, int sync);
 
        struct task_struct * (*pick_next_task) (struct rq *rq);
        void (*put_prev_task) (struct rq *rq, struct task_struct *p);

diff --git a/kernel/sched.c b/kernel/sched.c
index 98c0cdc..f01ff16 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -604,9 +604,9 @@ struct rq {
 
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
 
-static inline void check_preempt_curr(struct rq *rq, struct task_struct *p)
+static inline void check_preempt_curr(struct rq *rq, struct task_struct *p, int sync)
 {
-       rq->curr->sched_class->check_preempt_curr(rq, p);
+       rq->curr->sched_class->check_preempt_curr(rq, p, sync);
 }
 
 static inline int cpu_of(struct rq *rq)
@@ -2285,7 +2285,7 @@ out_running:
        trace_mark(kernel_sched_wakeup,
                "pid %d state %ld ## rq %p task %p rq->curr %p",
                p->pid, p->state, rq, p, rq->curr);
-       check_preempt_curr(rq, p);
+       check_preempt_curr(rq, p, sync);
 
        p->state = TASK_RUNNING;
 #ifdef CONFIG_SMP
@@ -2420,7 +2420,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
        trace_mark(kernel_sched_wakeup_new,
                "pid %d state %ld ## rq %p task %p rq->curr %p",
                p->pid, p->state, rq, p, rq->curr);
-       check_preempt_curr(rq, p);
+       check_preempt_curr(rq, p, 0);
 #ifdef CONFIG_SMP
        if (p->sched_class->task_wake_up)
                p->sched_class->task_wake_up(rq, p);
@@ -2880,7 +2880,7 @@ static void pull_task(struct rq *src_rq, struct task_struct *p,
         * Note that idle threads have a prio of MAX_PRIO, for this test
         * to be always true for them.
         */
-       check_preempt_curr(this_rq, p);
+       check_preempt_curr(this_rq, p, 0);
 }
 
 /*
@@ -5957,7 +5957,7 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
        set_task_cpu(p, dest_cpu);
        if (on_rq) {
                activate_task(rq_dest, p, 0);
-               check_preempt_curr(rq_dest, p);
+               check_preempt_curr(rq_dest, p, 0);
        }
 done:
        ret = 1;

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index fb8994c..ab8e6f3 100644 (file)
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1331,7 +1331,7 @@ static inline int depth_se(struct sched_entity *se)
 /*
  * Preempt the current task with a newly woken task if needed:
  */
-static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
+static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int sync)
 {
        struct task_struct *curr = rq->curr;
        struct cfs_rq *cfs_rq = task_cfs_rq(curr);
@@ -1360,6 +1360,13 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
        if (!sched_feat(WAKEUP_PREEMPT))
                return;
 
+       if (sched_feat(WAKEUP_OVERLAP) && sync &&
+                       se->avg_overlap < sysctl_sched_migration_cost &&
+                       pse->avg_overlap < sysctl_sched_migration_cost) {
+               resched_task(curr);
+               return;
+       }
+
        /*
         * preemption test can be made between sibling entities who are in the
         * same cfs_rq i.e who have a common parent. Walk up the hierarchy of
@@ -1642,7 +1649,7 @@ static void prio_changed_fair(struct rq *rq, struct task_struct *p,
                if (p->prio > oldprio)
                        resched_task(rq->curr);
        } else
-               check_preempt_curr(rq, p);
+               check_preempt_curr(rq, p, 0);
 }
 
 /*
@@ -1659,7 +1666,7 @@ static void switched_to_fair(struct rq *rq, struct task_struct *p,
        if (running)
                resched_task(rq->curr);
        else
-               check_preempt_curr(rq, p);
+               check_preempt_curr(rq, p, 0);
 }
 
 /* Account for a task changing its policy or group.

diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index c4c88ae..4e51893 100644 (file)
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -11,3 +11,4 @@ SCHED_FEAT(ASYM_GRAN, 1)
 SCHED_FEAT(LB_BIAS, 1)
 SCHED_FEAT(LB_WAKEUP_UPDATE, 1)
 SCHED_FEAT(ASYM_EFF_LOAD, 1)
+SCHED_FEAT(WAKEUP_OVERLAP, 1)

diff --git a/kernel/sched_idletask.c b/kernel/sched_idletask.c
index 3a4f92d..dec4cca 100644 (file)
--- a/kernel/sched_idletask.c
+++ b/kernel/sched_idletask.c
@@ -14,7 +14,7 @@ static int select_task_rq_idle(struct task_struct *p, int sync)
 /*
  * Idle tasks are unconditionally rescheduled:
  */
-static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p)
+static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int sync)
 {
        resched_task(rq->idle);
 }
@@ -76,7 +76,7 @@ static void switched_to_idle(struct rq *rq, struct task_struct *p,
        if (running)
                resched_task(rq->curr);
        else
-               check_preempt_curr(rq, p);
+               check_preempt_curr(rq, p, 0);
 }
 
 static void prio_changed_idle(struct rq *rq, struct task_struct *p,
@@ -93,7 +93,7 @@ static void prio_changed_idle(struct rq *rq, struct task_struct *p,
                if (p->prio > oldprio)
                        resched_task(rq->curr);
        } else
-               check_preempt_curr(rq, p);
+               check_preempt_curr(rq, p, 0);
 }
 
 /*

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 37f0721..68c4745 100644 (file)
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -784,7 +784,7 @@ static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
 /*
  * Preempt the current task with a newly woken task if needed:
  */
-static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p)
+static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p, int sync)
 {
        if (p->prio < rq->curr->prio) {
                resched_task(rq->curr);