linux-kernel - Re: [RFC v2 PATCH 2/8] sched: Maintain aggregated tasks count in cfs

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Date:	Wed, 14 Oct 2009 09:12:49 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Avi Kivity <avi@...hat.com>,
	Chris Friesen <cfriesen@...tel.com>,
	Paul Menage <menage@...gle.com>,
	Mike Waychison <mikew@...gle.com>
Subject: Re: [RFC v2 PATCH 2/8] sched: Maintain aggregated tasks count in
	cfs_rq at each hierarchy level

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.
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