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SubjectRe: [RFC, PATCH 1/2] sched: change the fairness model of the CFS group scheduler
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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.

> > > @@ -1100,6 +1127,27 @@ static void check_preempt_wakeup(struct
> > > if (!sched_feat(WAKEUP_PREEMPT))
> > > return;
> > >
> > > + /*
> > > + * preemption test can be made between sibling entities who are in the
> > > + * same cfs_rq i.e who have a common parent. Walk up the hierarchy of
> > > + * both tasks untill we find their ancestors who are siblings of common
> > > + * parent.
> > > + */
> > > +
> > > + /* First walk up until both entities are at same depth */
> > > + se_depth = depth_se(se);
> > > + pse_depth = depth_se(pse);
> > > +
> > > + while (se_depth > pse_depth) {
> > > + se_depth--;
> > > + se = parent_entity(se);
> > > + }
> > > +
> > > + while (pse_depth > se_depth) {
> > > + pse_depth--;
> > > + pse = parent_entity(pse);
> > > + }
> >
> > Sad, but needed.. for now..
> >
>
> better ideas if any are welcome! Cannot think of anything right now :(

Single rq can do without :-) If only I could get that latency isolation
going...



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