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

[Aaron Lu]

On Wed, Apr 10, 2019 at 10:18:10PM +0800, Aubrey Li wrote:
> On Wed, Apr 10, 2019 at 12:36 PM Aaron Lu <aaron.lu@xxxxxxxxxxxxxxxxx> 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?
> >
> > 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).
> >
> > 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.
> 
> Does it make sense if we take untagged tasks as hypervisor, and different
> cookie tasks as different VMs? Isolation is done between VMs, not between
> VM and hypervisor.
> 
> Did you see anything harmful if an untagged task and a tagged task
> run simultaneously on the same core?

VM can see hypervisor's data then, I think.
We probably do not want that happen.