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SubjectRe: [PATCH v2] sched/fair: Fix insertion in rq->leaf_cfs_rq_list
On Wed, Jan 30, 2019 at 02:06:20PM +0100, Peter Zijlstra wrote:
> On Wed, Jan 30, 2019 at 02:04:10PM +0100, Peter Zijlstra wrote:

> > So I don't much like this; at all. But maybe I misunderstand, this is
> > somewhat tricky stuff and I've not looked at it in a while.
> >
> > So per normal we do:
> >
> > enqueue_task_fair()
> > for_each_sched_entity() {
> > if (se->on_rq)
> > break;
> > enqueue_entity()
> > list_add_leaf_cfs_rq();
> > }
> >
> > This ensures that all parents are already enqueued, right? because this
> > is what enqueues those parents.
> >
> > And in this case you add an unconditional second
> > for_each_sched_entity(); even though it is completely redundant, afaict.
>
> Ah, it doesn't do a second iteration; it continues where the previous
> two left off.
>
> Still, why isn't this in unthrottle?

Aah, I see, because we need:

rq->tmp_alone_branch == &rq->lead_cfs_rq_list

at the end of enqueue_task_fair(); having had that assertion would've
saved some pain I suppose.

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