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authorLiang Chen <cl@rock-chips.com>2020-03-06 15:01:33 +0800
committerPeter Zijlstra <peterz@infradead.org>2020-03-20 13:06:20 +0100
commit26c7295be0c5e6da3fa45970e9748be983175b1b (patch)
treef8343709aea173894a49fd741a90819c5e2c09b8 /kernel/kthread.c
parentc32b4308295aaaaedd5beae56cb42e205ae63e58 (diff)
kthread: Do not preempt current task if it is going to call schedule()
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
Diffstat (limited to 'kernel/kthread.c')
-rw-r--r--kernel/kthread.c17
1 files changed, 15 insertions, 2 deletions
diff --git a/kernel/kthread.c b/kernel/kthread.c
index b262f47046ca..bfbfa481be3a 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -199,8 +199,15 @@ 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);
}
@@ -245,8 +252,14 @@ 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)) {