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sched: wakeup preempt when small overlap

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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>
This commit is contained in:
Peter Zijlstra 2008-09-20 23:38:02 +02:00 • committed by Ingo Molnar
parent 09b22a2f67
commit 15afe09bf4
6 changed files with 22 additions and 14 deletions
Download patch file Download diff file Expand all files Collapse all files

12
kernel/sched.c
View file

@ -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)
@ -2282,7 +2282,7 @@ 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
@ -2417,7 +2417,7 @@ 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);
@ -2877,7 +2877,7 @@ 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);
}
/*
@ -6007,7 +6007,7 @@ 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;