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kthread: do not preempt current task if it is going to call schedule()

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when we create a kthread with ktrhead_create_on_cpu(),the child thread
entry is ktread.c:ktrhead() which will be preempted by the parent after
call complete(done) while schedule() is not called yet,then the parent
will call wait_task_inactive(child) but the child is still on the runqueue,
so the parent will schedule_hrtimeout() for 1 jiffy,it will waste a lot of
time,especially on startup.

  parent                             child
ktrhead_create_on_cpu()
  wait_fo_completion(&done) -----> ktread.c:ktrhead()
                             |----- complete(done);--wakeup and preempted by parent
 kthread_bind() <------------|  |-> schedule();--dequeue here
  wait_task_inactive(child)     |
   schedule_hrtimeout(1 jiffy) -|

So we hope the child just wakeup parent but not preempted by parent, and the
child is going to call schedule() soon,then the parent will not call
schedule_hrtimeout(1 jiffy) as the child is already dequeue.

The same issue for ktrhead_park()&&kthread_parkme().
This patch can save 120ms on rk312x startup with CONFIG_HZ=300.

Change-Id: I2ae4edb538ea6f55cf5b8f8b5dc6311d1811a4ae
Signed-off-by: Liang Chen <cl@rock-chips.com>
This commit is contained in:
Liang Chen
2020-03-05 11:52:56 +08:00
committed by Tao Huang
parent b1ae882b40
commit 3be6453a90
1 changed files with 15 additions and 2 deletions
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17
kernel/kthread.c
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@@ -191,8 +191,15 @@ static void __kthread_parkme(struct kthread *self)
if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
break;
/*
* Thread is going to call schedule(), do not preempt it,
* or the caller of kthread_park() may spend more time in
* wait_task_inactive().
*/
preempt_disable();
complete(&self->parked);
schedule();
schedule_preempt_disabled();
preempt_enable();
}
__set_current_state(TASK_RUNNING);
}
@@ -237,8 +244,14 @@ static int kthread(void *_create)
/* OK, tell user we're spawned, wait for stop or wakeup */
__set_current_state(TASK_UNINTERRUPTIBLE);
create->result = current;
/*
* Thread is going to call schedule(), do not preempt it,
* or the creator may spend more time in wait_task_inactive().
*/
preempt_disable();
complete(done);
schedule();
schedule_preempt_disabled();
preempt_enable();
ret = -EINTR;
if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {