sched: wakeup preempt when small overlap
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>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b3b7a8f..d8e699b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -897,7 +897,7 @@
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 0d8905a..ad9d39b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -604,9 +604,9 @@
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)
@@ -2282,7 +2282,7 @@
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
@@ -2417,7 +2417,7 @@
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);
@@ -2877,7 +2877,7 @@
* 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);
}
/*
@@ -6007,7 +6007,7 @@
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 a10ac0b..7328383 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1331,7 +1331,7 @@
/*
* 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);
@@ -1367,6 +1367,13 @@
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
@@ -1649,7 +1656,7 @@
if (p->prio > oldprio)
resched_task(rq->curr);
} else
- check_preempt_curr(rq, p);
+ check_preempt_curr(rq, p, 0);
}
/*
@@ -1666,7 +1673,7 @@
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 9353ca7..bf027a7 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -11,3 +11,4 @@
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
--- a/kernel/sched_idletask.c
+++ b/kernel/sched_idletask.c
@@ -14,7 +14,7 @@
/*
* 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 @@
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 @@
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 5523107..6d2d0a5d 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -783,7 +783,7 @@
/*
* 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);