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

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Date:   Thu, 11 Apr 2019 10:11:53 +0800
From:   Aaron Lu <aaron.lu@...ux.alibaba.com>
To:     Aubrey Li <aubrey.intel@...il.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Subhra Mazumdar <subhra.mazumdar@...cle.com>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>,
        Julien Desfossez <jdesfossez@...italocean.com>
Subject: Re: [RFC][PATCH 13/16] sched: Add core wide task selection and
 scheduling.

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@...ux.alibaba.com> 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.