update vruntime incorrectly When use rt_mutex
Kathleen Chang
yt.chang at mediatek.com
Tue Mar 20 22:52:06 PDT 2018
hi,
Thanks for your feedback.
On Fri, 2018-03-16 at 10:51 +0100, Peter Zijlstra wrote:
> On Thu, Mar 15, 2018 at 03:36:10PM +0800, Kathleen Chang wrote:
> > hi,
> >
> > We found the vruntime might update incorrectly when use rt_mutex.
>
> That's nice, on what kernel?
>
> Also, your email is very hard to make sense of.
>
> > <<abnormal case>>
> > When the Task is waking, update vruntime incorrectly.
> > 1. When there is a CFS task (A) hold rt_mutex_lock and the state is
> > TASK_WAKING (on_rq=0), a RT task (B) want to hold this rt_mutex_lock.
> > Update vruntime incorrectly.
> >
> > RT task (B)
> > rt_mutex_setprio (cfs->RT) -> Task is waking , and update
> > vruntime
> >
> > queued = task_on_rq_queued(p); // task is waking, queued=0
> > running = task_current(rq, p);
> > if (queued) /* don't update vruntime here! */
> > dequeue_task(rq, p, queue_flag);
> > if (running)
> > put_prev_task(rq, p);
> >
> > check_class_changed(rq, p, prev_class, oldprio); ->
> > switched_from_fair ->
> > detach_task_cfs_rq
> > ( due to task is waking, and bypass
> > vruntime-=cfs_rq.min_vruntime)
> >
> > static void detach_task_cfs_rq(struct task_struct *p)
> > {
> > struct sched_entity *se = &p->se;
> > struct cfs_rq *cfs_rq = cfs_rq_of(se);
> >
> > if (!vruntime_normalized(p)) { // return 1, then p->state is
> > TASK_WAKING
> > /*
> > * Fix up our vruntime so that the current sleep doesn't
> > * cause 'unlimited' sleep bonus.
> > */
> > place_entity(cfs_rq, se, 0);
> > check_vruntime(8, se, cfs_rq->min_vruntime);
> > se->vruntime -= cfs_rq->min_vruntime;
>
> So here we subtract min_vruntime,
When the p->state is TASK_WAKING, vruntime_normlized will return 1
and if(!vruntime_normalized(p)) will be 0
in this case, don't subtract min_vruntime.
>
> > se->normalized = true;
>
> this doesn't exist.. which makes me wonder what you're looking at,
>
> > }
> >
> > detach_entity_cfs_rq(se);
> > }
> >
> > // when p->state is TASK_WAKING, the task's vruntime is normalized
> > static inline bool vruntime_normalized(struct task_struct *p)
> > {
> > .....
> > if (!se->sum_exec_runtime || p->state == TASK_WAKING)
> > return true;
> >
> > }
> >
> > 2. When the task (A) which holds the rt_muex_lock unlock the
> > rt_mutex_lock.
> > Task (A) must be on_rq=1
> >
> > rt_mutex_setprio (RT->CFS)
> > if (queued)
> > enqueue_task(rq, p, queue_flag); );
> > /* vruntime += cfs_rq.min_vruntime */
>
> And here we're adding min_vruntime.
>
> > if (running)
> > set_curr_task(rq, p);
> >
> > that result in vruntime accumulates
>
> So what exactly is the problem?
>
>
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