Re: [RFC][PATCH 13/16] sched: Add core wide task selection and scheduling.

[Peter Zijlstra]

On Wed, Apr 10, 2019 at 12:36:33PM +0800, Aaron Lu wrote:
> On Tue, Apr 09, 2019 at 11:09:45AM -0700, Tim Chen wrote:
> > Now that we have accumulated quite a number of different fixes to your orginal
> > posted patches.  Would you like to post a v2 of the core scheduler with the fixes?
> 
> One more question I'm not sure: should a task with cookie=0, i.e. tasks
> that are untagged, be allowed to scheduled on the the same core with
> another tagged task?

That was not meant to be possible.

> The current patch seems to disagree on this, e.g. in pick_task(),
> if max is already chosen but max->core_cookie == 0, then we didn't care
> about cookie and simply use class_pick for the other cpu. This means we
> could schedule two tasks with different cookies(one is zero and the
> other can be tagged).

When core_cookie==0 we shouldn't schedule the other siblings at all.

> But then sched_core_find() only allow idle task to match with any tagged
> tasks(we didn't place untagged tasks to the core tree of course :-).
> 
> Thoughts? Do I understand this correctly? If so, I think we probably
> want to make this clear before v2. I personally feel, we shouldn't allow
> untagged tasks(like kernel threads) to match with tagged tasks.

Agreed, cookie should always match or idle.