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

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Message-ID: <CAERHkrsKMm7f2auaQwY5=rodQr5T0kbOo2N1DCUCQcuUOpsEMg@mail.gmail.com>
Date:   Wed, 10 Apr 2019 22:18:10 +0800
From:   Aubrey Li <aubrey.intel@...il.com>
To:     Aaron Lu <aaron.lu@...ux.alibaba.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>,
        Aubrey Li <aubrey.intel@...il.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 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?

Thanks,
-Aubrey