Re: [RFC v2 PATCH 2/8] sched: Maintain aggregated tasks count in cfs_rq at each hierarchy level

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Tue, Oct 13, 2009 at 04:27:01PM +0200, Peter Zijlstra wrote:
> On Wed, 2009-09-30 at 18:21 +0530, Bharata B Rao wrote:
> 
> > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> > index 652e8bd..eeeddb8 100644
> > --- a/kernel/sched_fair.c
> > +++ b/kernel/sched_fair.c
> > @@ -243,6 +243,27 @@ find_matching_se(struct sched_entity **se, struct sched_entity **pse)
> >  
> >  #endif	/* CONFIG_FAIR_GROUP_SCHED */
> >  
> > +static void add_cfs_rq_tasks_running(struct sched_entity *se,
> > +		unsigned long count)
> > +{
> > +	struct cfs_rq *cfs_rq;
> > +
> > +	for_each_sched_entity(se) {
> > +		cfs_rq = cfs_rq_of(se);
> > +		cfs_rq->nr_tasks_running += count;
> > +	}
> > +}
> > +
> > +static void sub_cfs_rq_tasks_running(struct sched_entity *se,
> > +		unsigned long count)
> > +{
> > +	struct cfs_rq *cfs_rq;
> > +
> > +	for_each_sched_entity(se) {
> > +		cfs_rq = cfs_rq_of(se);
> > +		cfs_rq->nr_tasks_running -= count;
> > +	}
> > +}
> >  
> >  /**************************************************************
> >   * Scheduling class tree data structure manipulation methods:
> > @@ -969,6 +990,7 @@ static void enqueue_task_fair(struct rq *rq, struct task_struct *p, int wakeup)
> >  		wakeup = 1;
> >  	}
> >  
> > +	add_cfs_rq_tasks_running(&p->se, 1);
> >  	hrtick_update(rq);
> >  }
> >  
> > @@ -991,6 +1013,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int sleep)
> >  		sleep = 1;
> >  	}
> >  
> > +	sub_cfs_rq_tasks_running(&p->se, 1);
> >  	hrtick_update(rq);
> >  }
> 
> This seems daft, why not add the incement to the for_each_sched_entity()
> loop already present in both functions?

Right. There was a reason why it started out like this and I can't seem to
remember. Now looking at the current code, I don't see why I can't do what
you suggest. Will try this for the next post.

Regards,
Bharata.