linux-kernel - Re: [RFC, PATCH 1/2] sched: change the fairness model of the CFS group scheduler

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Message-ID: <20080304094944.GB3730@linux.vnet.ibm.com>
Date:	Tue, 4 Mar 2008 15:19:44 +0530
From:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ibm.com>,
	Aneesh Kumar KV <aneesh.kumar@...ux.vnet.ibm.com>,
	lkml <linux-kernel@...r.kernel.org>, vgoyal@...hat.com,
	serue@...ibm.com, menage@...gle.com
Subject: Re: [RFC, PATCH 1/2] sched: change the fairness model of the CFS
	group scheduler

On Fri, Feb 29, 2008 at 11:37:55AM +0100, Peter Zijlstra wrote:
> 
> On Fri, 2008-02-29 at 14:34 +0530, Dhaval Giani wrote:
> 
> > > > +#elif defined CONFIG_USER_SCHED
> > > > +		/*
> > > > +		 * In case of task-groups formed thr' the user id of tasks,
> > > > +		 * init_task_group represents tasks belonging to root user.
> > > > +		 * Hence it forms a sibling of all subsequent groups formed.
> > > > +		 * In this case, init_task_group gets only a fraction of overall
> > > > +		 * system cpu resource, based on the weight assigned to root
> > > > +		 * user's cpu share (INIT_TASK_GROUP_LOAD). This is accomplished
> > > > +		 * by letting tasks of init_task_group sit in a separate cfs_rq
> > > > +		 * (init_cfs_rq) and having one entity represent this group of
> > > > +		 * tasks in rq->cfs (i.e init_task_group->se[] != NULL).
> > > > +		 */
> > > >  		init_tg_cfs_entry(rq, &init_task_group,
> > > >  				&per_cpu(init_cfs_rq, i),
> > > >  				&per_cpu(init_sched_entity, i), i, 1);
> > > 
> > > But I fail to parse this lengthy comment. What does it do:
> > > 
> > >     init_group
> > >    /     |    \
> > > uid-0 uid-1000 uid-n
> > > 
> > > or does it blend uid-0 into the init_group?
> > > 
> > 
> > It blends uid-0 (root) into init_group.
> 
> Any particular reason why? It seems to me uid-0 should be treated like
> any other uid.
> 

Ah, I misunderstood your question. We have not changed anything for UID
scheduling as no task can (should) exist at the root level (init_group).
Your initial figure is right, sorry for the confusion.

Thanks,
-- 
regards,
Dhaval
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