Re: [PATCH v2] sched: let __sched_period() use rq's nr_running

[Byungchul Park]

On Mon, Jul 13, 2015 at 10:26:09AM +0200, Peter Zijlstra wrote:
> On Fri, Jul 10, 2015 at 05:11:30PM +0900, byungchul.park@xxxxxxx wrote:
> > From: Byungchul Park <byungchul.park@xxxxxxx>
> > 
> > __sched_period() returns a period which a rq can have. the period has to be
> > stretched by the number of task *the rq has*, when nr_running > nr_latency.
> > otherwise, task slice can be very smaller than sysctl_sched_min_granularity
> > depending on the position of tg hierarchy when CONFIG_FAIR_GROUP_SCHED.
> > 
> > Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
> > ---
> >  kernel/sched/fair.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 09456fc..8ae7aeb 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -635,7 +635,7 @@ static u64 __sched_period(unsigned long nr_running)
> >   */
> >  static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
> >  {
> > -	u64 slice = __sched_period(cfs_rq->nr_running + !se->on_rq);
> > +	u64 slice = __sched_period(rq_of(cfs_rq)->nr_running + !se->on_rq);
> >  
> >  	for_each_sched_entity(se) {
> >  		struct load_weight *load;
> 
> This really doesn't make sense; look at what that
> for_each_sched_entity() loop does below this.

hello,

for_each_sched_entity() loop is distributing slice to se with consideration
for both hierarchy and its weight, walking from the passed se to the top rq. 

i am just talking about how to get a whole period value. my question is 
"why does it use local cfs's nr_running to get a whole period value?".

> 
> I agree that sched_slice() is a difficult proposition in the face of
> cgroup, but everything is, cgroups suck arse, they make everything hard.

i don't make an issue of the way for cgroups to work though it already have
many problems as you said.

thank you for commenting,
byungchul

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