kthread: Do not preempt current task if it is going to call schedule()
commit 26c7295be0
upstream.
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.
Signed-off-by: Liang Chen <cl@rock-chips.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lkml.kernel.org/r/20200306070133.18335-2-cl@rock-chips.com
Signed-off-by: Chanho Park <chanho61.park@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
504fe0ab24
commit
52d322f919
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@ -199,8 +199,15 @@ static void __kthread_parkme(struct kthread *self)
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if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
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if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
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break;
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break;
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/*
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* Thread is going to call schedule(), do not preempt it,
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* or the caller of kthread_park() may spend more time in
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* wait_task_inactive().
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*/
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preempt_disable();
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complete(&self->parked);
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complete(&self->parked);
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schedule();
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schedule_preempt_disabled();
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preempt_enable();
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}
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}
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__set_current_state(TASK_RUNNING);
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__set_current_state(TASK_RUNNING);
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}
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}
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@ -245,8 +252,14 @@ static int kthread(void *_create)
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/* OK, tell user we're spawned, wait for stop or wakeup */
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/* OK, tell user we're spawned, wait for stop or wakeup */
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__set_current_state(TASK_UNINTERRUPTIBLE);
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__set_current_state(TASK_UNINTERRUPTIBLE);
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create->result = current;
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create->result = current;
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/*
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* Thread is going to call schedule(), do not preempt it,
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* or the creator may spend more time in wait_task_inactive().
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*/
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preempt_disable();
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complete(done);
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complete(done);
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schedule();
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schedule_preempt_disabled();
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preempt_enable();
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ret = -EINTR;
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ret = -EINTR;
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if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
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if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
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