Messages in this thread | | | Subject | Re: update vruntime incorrectly When use rt_mutex | From | Kathleen Chang <> | Date | Wed, 21 Mar 2018 13:52:06 +0800 |
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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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