Re: [PATCH] Revert "sched/fair: Fix O(nr_cgroups) in the load balancing path"

[Srinivas Pandruvada]

On Tue, 2019-10-29 at 12:34 -0700, Srinivas Pandruvada wrote:
> On Fri, 2019-10-25 at 08:55 -0700, Doug Smythies wrote:
> 
> [...]
> 
> > Experiment method:
> > 
> > enable only idle state 1
> > Dountil stopped
> >   apply a 100% load (all CPUs)
> >   after awhile (about 50 seconds) remove the load.
> >   allow a short transient delay (1 second).
> >   measure the processor package joules used over the next 149
> > seconds.
> > Enduntil
> > 
> > Kernel k5.4-rc2 + reversion (this method)
> > Average processor package power: 9.148 watts (128 samples, > 7
> > hours)
> > Minimum: 9.02 watts
> > Maximum: 9.29 watts
> > Note: outlyer data point group removed, as it was assumed the
> > computer
> > had something to do and wasn't actually "idle".
> > 
> > Kernel 5.4-rc2:
> > Average processor package power: 9.969 watts (150 samples, > 8
> > hours)
> > Or 9% more energy for the idle phases of the work load.
> > Minimum: 9.15 watts
> > Maximum: 13.79 watts (51% more power)
> 
> Hi Doug,
> 
> Do you have intel_pstate_tracer output? I guess that when started
> request to measure the measure joules, it started at higher P-state
> without revert.
> Other way is check by fixing the max and min scaling frequency to
> some
> frequency, then we shouldn't see power difference.
I mean not significant power difference. Also to get real numbers, need
to use some power meter measuring CPU power. If I can get your script,
I may be able to measure that.

Thanks,
Srinivas

> 
> Thanks,
> Srinivas
> 
> 
> > 
> > ---
> >  kernel/sched/fair.c | 43 +++++++++------------------------------
> > ----
> >  1 file changed, 9 insertions(+), 34 deletions(-)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 83ab35e..51625b8 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -381,10 +381,9 @@ static inline void
> > assert_list_leaf_cfs_rq(struct rq *rq)
> >  	SCHED_WARN_ON(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list);
> >  }
> >  
> > -/* Iterate thr' all leaf cfs_rq's on a runqueue */
> > -#define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos)			
> > \
> > -	list_for_each_entry_safe(cfs_rq, pos, &rq->leaf_cfs_rq_list,	
> > \
> > -				 leaf_cfs_rq_list)
> > +/* Iterate through all cfs_rq's on a runqueue in bottom-up order
> > */
> > +#define for_each_leaf_cfs_rq(rq, cfs_rq) \
> > +	list_for_each_entry_rcu(cfs_rq, &rq->leaf_cfs_rq_list,
> > leaf_cfs_rq_list)
> >  
> >  /* Do the two (enqueued) entities belong to the same group ? */
> >  static inline struct cfs_rq *
> > @@ -481,8 +480,8 @@ static inline void
> > assert_list_leaf_cfs_rq(struct
> > rq *rq)
> >  {
> >  }
> >  
> > -#define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos)	\
> > -		for (cfs_rq = &rq->cfs, pos = NULL; cfs_rq; cfs_rq =
> > pos)
> > +#define for_each_leaf_cfs_rq(rq, cfs_rq)	\
> > +		for (cfs_rq = &rq->cfs; cfs_rq; cfs_rq = NULL)
> >  
> >  static inline struct sched_entity *parent_entity(struct
> > sched_entity
> > *se)
> >  {
> > @@ -7502,27 +7501,10 @@ static inline void
> > update_blocked_load_status(struct rq *rq, bool has_blocked) {
> >  
> >  #ifdef CONFIG_FAIR_GROUP_SCHED
> >  
> > -static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
> > -{
> > -	if (cfs_rq->load.weight)
> > -		return false;
> > -
> > -	if (cfs_rq->avg.load_sum)
> > -		return false;
> > -
> > -	if (cfs_rq->avg.util_sum)
> > -		return false;
> > -
> > -	if (cfs_rq->avg.runnable_load_sum)
> > -		return false;
> > -
> > -	return true;
> > -}
> > -
> >  static void update_blocked_averages(int cpu)
> >  {
> >  	struct rq *rq = cpu_rq(cpu);
> > -	struct cfs_rq *cfs_rq, *pos;
> > +	struct cfs_rq *cfs_rq;
> >  	const struct sched_class *curr_class;
> >  	struct rq_flags rf;
> >  	bool done = true;
> > @@ -7534,7 +7516,7 @@ static void update_blocked_averages(int cpu)
> >  	 * Iterates the task_group tree in a bottom up fashion, see
> >  	 * list_add_leaf_cfs_rq() for details.
> >  	 */
> > -	for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos) {
> > +	for_each_leaf_cfs_rq(rq, cfs_rq) {
> >  		struct sched_entity *se;
> >  
> >  		if (update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq),
> > cfs_rq))
> > @@ -7545,13 +7527,6 @@ static void update_blocked_averages(int cpu)
> >  		if (se && !skip_blocked_update(se))
> >  			update_load_avg(cfs_rq_of(se), se, 0);
> >  
> > -		/*
> > -		 * There can be a lot of idle CPU cgroups.  Don't let
> > fully
> > -		 * decayed cfs_rqs linger on the list.
> > -		 */
> > -		if (cfs_rq_is_decayed(cfs_rq))
> > -			list_del_leaf_cfs_rq(cfs_rq);
> > -
> >  		/* Don't need periodic decay once load/util_avg are
> > null */
> >  		if (cfs_rq_has_blocked(cfs_rq))
> >  			done = false;
> > @@ -10444,10 +10419,10 @@ const struct sched_class fair_sched_class
> > =
> > {
> >  #ifdef CONFIG_SCHED_DEBUG
> >  void print_cfs_stats(struct seq_file *m, int cpu)
> >  {
> > -	struct cfs_rq *cfs_rq, *pos;
> > +	struct cfs_rq *cfs_rq;
> >  
> >  	rcu_read_lock();
> > -	for_each_leaf_cfs_rq_safe(cpu_rq(cpu), cfs_rq, pos)
> > +	for_each_leaf_cfs_rq(cpu_rq(cpu), cfs_rq)
> >  		print_cfs_rq(m, cpu, cfs_rq);
> >  	rcu_read_unlock();
> >  }
> 
>