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

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Date:   Wed, 10 Apr 2019 12:36:33 +0800
From:   Aaron Lu <aaron.lu@...ux.alibaba.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, tglx@...utronix.de, pjt@...gle.com,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        subhra.mazumdar@...cle.com, fweisbec@...il.com,
        keescook@...omium.org, 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 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.