Re: oltp ~10% regression with 2.6.27-rc5 on stoakley machine

From: Peter Zijlstra
Date: Sat Sep 20 2008 - 17:38:34 EST

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>
> ------- Comment #4 from ming.m.lin@xxxxxxxxx 2008-09-17 17:55 -------
> sched_switch trace of oltp in 2.6.27-rc4
> http://myfreefilehosting.com/f/fc6c8eaacf_1.31MB
>
> sched_switch trace of oltp in 2.6.27-rc5
> http://myfreefilehosting.com/f/a2f9aea1b0_0.42MB
>
> Compared the 2 trace files, you can find that (at most time),
> with 2.6.27-rc5, mysql switches to sysbench when it's going to sleep
> mysqld-3791 [07] 151.421836: 3791:120:R + 3803:120:S
> mysqld-3791 [07] 151.421876: 3791:120:S ==> 3803:120:R
> sysbench-3803 [07] 151.421878: 3803:120:R + 3791:120:S
> sysbench-3803 [07] 151.421887: 3803:120:S ==> 3791:120:R
>
> with 2.6.27-rc4, mysql switches to sysbench when it's still running
> mysqld-3674 [07] 95.960220: 3674:120:R + 3687:120:S
> mysqld-3674 [07] 95.960220: 3674:120:R ==> 3687:120:R
> sysbench-3687 [07] 95.960220: 3687:120:S ==> 3674:120:R
>
> So with 2.6.27-rc5, sysbench wakes up mysql and then switches to it (mysql is
> in sleep state)
>
> With 2.6.27-rc4, sysbench switches to mysql, no need to wake up it (mysql is
> still in running state)

Ming, how does this work for you?

---
Subject: sched: wakeup preempt when small overlap

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.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7b4592c..cb44774 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -897,7 +897,7 @@ 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 32d56d6..e17d506 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -609,9 +609,9 @@ 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)
@@ -2299,7 +2299,7 @@ out_activate:

out_running:
trace_sched_wakeup(rq, p);
- check_preempt_curr(rq, p);
+ check_preempt_curr(rq, p, sync);

p->state = TASK_RUNNING;
#ifdef CONFIG_SMP
@@ -2432,7 +2432,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
inc_nr_running(rq);
}
trace_sched_wakeup_new(rq, p);
- 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);
@@ -2889,7 +2889,7 @@ 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);
}

/*
@@ -6015,7 +6015,7 @@ 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 a10ac0b..82a907c 100644
--- 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);
@@ -1348,6 +1348,8 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
if (unlikely(se == pse))
return;

+ cfs_rq_of(pse)->next = pse;
+
/*
* We can come here with TIF_NEED_RESCHED already set from new task
* wake up path.
@@ -1355,8 +1357,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
if (test_tsk_need_resched(curr))
return;

- cfs_rq_of(pse)->next = pse;
-
/*
* Batch tasks do not preempt (their preemption is driven by
* the tick):
@@ -1367,6 +1367,13 @@ 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
@@ -1649,7 +1656,7 @@ 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);
}

/*
@@ -1666,7 +1673,7 @@ 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 9353ca7..bf027a7 100644
--- 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
--- 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 04875ef..2e228bd 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -787,7 +787,7 @@ 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);

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Next message: Dan Williams: "Re: [PATCH] dmatest: properly handle duplicate DMA channels"
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