> >
> > ------- Comment #4 from
ming.m.lin@intel.com 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@chello.nl>
> ---
> 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);
>
>
