Hi Peter,
While I am checking the preempt related code, I find a interesting part.
That is when preempt_schedule is called, for its preempt_count be added
PREEMPT_ACTIVE, so in __schedule() it could not be dequeued from rq
by deactivate_task.
Thus in put_prev_task, which is called a little later in __schedule(), it
would call put_prev_task_fair, which finally calls put_prev_entity.
For current task is not dequeued from rq, so in this function, it would
enqueue it again to the rq by __enqueue_entity.
Is there any reason to do like this, since entity already is over rq,
why need to queue it again?
And if current rq's vruntime distribution like below, and vruntime with 8
is the task that would be get preempted. So in __enqueue_entity,
its rb_left/rb_right would be set as NULL and reinserted into this RB tree.
Then seems to me now, the entity with vruntime of 3 would be disappeared
from the RB tree.
13
/ \
8 19
/ \
3 11
I am not sure whether I understand the whole process correctly...
Would the example as above happen in our real life?
Thanks,
Lei
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