On Tue, Sep 01, 2015 at 09:28:49AM +0900, Byungchul Park wrote:
> check the condition "!(flags & DEQUEUE_SLEEP)" for doing normalizing in
> dequeue_entity(). i think you have to keep my original comment, or
> modify your comment to something like below.
>
> before - If it's !queued, sleeping tasks have a normalized vruntime,
> after - If it's !queued, sleeping tasks have a non-normalize vruntime,
>
> but.. i think it would be better that you keep my original comment..
The comment we can talk about later, but I think the condition:
> > - if (p->state == TASK_RUNNING)
> > + if (!p->se.on_rq)
is important now. Both are broken in different ways.
p->state == TASK_RUNNING
is broken in this scenario:
CPU0 CPU1
set_current_state(TASK_UNINTERRUPTIBLE);
sched_move_task()
task_move_group_fair()
vruntime_normalized() ==
true
if (!cond)
schedule();
__set_current_state(TASK_RUNNING);
Now the proposed replacement:
!p->se.on_rq
is equally broken, because (as you point out) clearing it isn't
conditional on DEQUEUE_SLEEP.
And the problem with tracking the vruntime state is that while it helps
detach_task_cfs_rq(), attach_task_cfs_rq() is still left wondering what
it should return to.
So we do indeed need something to determine, based on the current state,
if vruntime should be normalized.
/me ponders moar
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