Date: Sat, 15 Aug 2015 17:21:07 +0900
From: Byungchul Park <byungchul.park@lge.com>
To: "T. Zhou" <t.s.zhou@hotmail.com>
Cc: mingo@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org,
        yuyang.du@intel.com
Subject: Re: [PATCH 2/2] sched: make task_move_group_fair simple by using
 switched_to(from)_fair
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On Fri, Aug 14, 2015 at 10:50:34PM +0800, T. Zhou wrote:
> Hi,
> 
> On Thu, Aug 13, 2015 at 07:49:19PM +0900, byungchul.park@lge.com wrote:
> > +static inline int need_vruntime_adjust(struct task_struct *p, int queued)
> > +{
> > +	struct sched_entity *se = &p->se;
> > +
> > +	/*
> > +	 * When !queued, vruntime of the task has usually NOT been normalized.
> > +	 * But there are some cases where it has already been normalized:
> > +	 *
> > +	 * - Moving a forked child which is waiting for being woken up by
> > +	 *   wake_up_new_task().
> > +	 * - Moving a task which has been woken up by try_to_wake_up() and
> > +	 *   waiting for actually being woken up by sched_ttwu_pending().
> > +	 */
> > +	if (queued)
> > +		return 0;
> > +
> > +	if (!se->sum_exec_runtime || p->state == TASK_WAKING)
> > +		return 0;
> > +
> > +	if (p->state != TASK_RUNNING)
> > +		return 1;
> > +
> > +	return 0;
> > +}
> 
> Original switched_from/to_fair() do not include the following check.
> 
> 	if (!se->sum_exec_runtime || p->state == TASK_WAKING)
> 		return 0;
> 
> I guess you're sure this check will always fail in switched_from/to_fair() case

hello,

i wanted to introduce a function for checking necessity of adjusting
vruntime in general which may be also used in future. :)

thanks,
byungchul

> 
> Thanks
> >  static void switched_from_fair(struct rq *rq, struct task_struct *p)
> >  {
> >  	struct sched_entity *se = &p->se;
> > @@ -7918,7 +7943,7 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
> >  	 * have normalized the vruntime, if it's !queued, then only when
> >  	 * the task is sleeping will it still have non-normalized vruntime.
> >  	 */
> > -	if (!task_on_rq_queued(p) && p->state != TASK_RUNNING) {
> > +	if (need_vruntime_adjust(p, task_on_rq_queued(p))) {
> >  		/*
> >  		 * Fix up our vruntime so that the current sleep doesn't
> >  		 * cause 'unlimited' sleep bonus.
> > @@ -7939,7 +7964,6 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
> >  static void switched_to_fair(struct rq *rq, struct task_struct *p)
> >  {
> >  	struct sched_entity *se = &p->se;
> > -
> >  #ifdef CONFIG_FAIR_GROUP_SCHED
> >  	/*
> >  	 * Since the real-depth could have been changed (only FAIR
> > @@ -7964,7 +7988,7 @@ static void switched_to_fair(struct rq *rq, struct task_struct *p)
> >  		 * has non-normalized vruntime, if it's !queued, then it still has
> >  		 * normalized vruntime.
> >  		 */
> > -		if (p->state != TASK_RUNNING)
> > +		if (need_vruntime_adjust(p, task_on_rq_queued(p)))
> >  			se->vruntime += cfs_rq_of(se)->min_vruntime;
> >  		return;
> >  	}
> > @@ -8014,55 +8038,9 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
> >  #ifdef CONFIG_FAIR_GROUP_SCHED
> >  static void task_move_group_fair(struct task_struct *p, int queued)
> >  {
> > -	struct sched_entity *se = &p->se;
> > -	struct cfs_rq *cfs_rq;
> > -
> > -	/*
> > -	 * If the task was not on the rq at the time of this cgroup movement
> > -	 * it must have been asleep, sleeping tasks keep their ->vruntime
> > -	 * absolute on their old rq until wakeup (needed for the fair sleeper
> > -	 * bonus in place_entity()).
> > -	 *
> > -	 * If it was on the rq, we've just 'preempted' it, which does convert
> > -	 * ->vruntime to a relative base.
> > -	 *
> > -	 * Make sure both cases convert their relative position when migrating
> > -	 * to another cgroup's rq. This does somewhat interfere with the
> > -	 * fair sleeper stuff for the first placement, but who cares.
> > -	 */
> > -	/*
> > -	 * When !queued, vruntime of the task has usually NOT been normalized.
> > -	 * But there are some cases where it has already been normalized:
> > -	 *
> > -	 * - Moving a forked child which is waiting for being woken up by
> > -	 *   wake_up_new_task().
> > -	 * - Moving a task which has been woken up by try_to_wake_up() and
> > -	 *   waiting for actually being woken up by sched_ttwu_pending().
> > -	 *
> > -	 * To prevent boost or penalty in the new cfs_rq caused by delta
> > -	 * min_vruntime between the two cfs_rqs, we skip vruntime adjustment.
> > -	 */
> > -	if (!queued && (!se->sum_exec_runtime || p->state == TASK_WAKING))
> > -		queued = 1;
> > -
> > -	cfs_rq = cfs_rq_of(se);
> > -	if (!queued)
> > -		se->vruntime -= cfs_rq->min_vruntime;
> > -
> > -#ifdef CONFIG_SMP
> > -	/* synchronize task with its prev cfs_rq */
> > -	detach_entity_load_avg(cfs_rq, se);
> > -#endif
> > +	switched_from_fair(task_rq(p), p);
> >  	set_task_rq(p, task_cpu(p));
> > -	se->depth = se->parent ? se->parent->depth + 1 : 0;
> > -	cfs_rq = cfs_rq_of(se);
> > -	if (!queued)
> > -		se->vruntime += cfs_rq->min_vruntime;
> > -
> > -#ifdef CONFIG_SMP
> > -	/* Virtually synchronize task with its new cfs_rq */
> > -	attach_entity_load_avg(cfs_rq, se);
> > -#endif
> > +	switched_to_fair(task_rq(p), p);
> >  }
> >  
> >  void free_fair_sched_group(struct task_group *tg)
> 
> -- 
> Tao
> --
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