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

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Date:   Thu, 11 Apr 2019 11:19:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Aaron Lu <aaron.lu@...ux.alibaba.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>, 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 Thu, Apr 11, 2019 at 11:05:41AM +0800, Aaron Lu wrote:
> On Wed, Apr 10, 2019 at 04:44:18PM +0200, Peter Zijlstra wrote:
> > When core_cookie==0 we shouldn't schedule the other siblings at all.
> 
> Not even with another untagged task?
> 
> I was thinking to leave host side tasks untagged, like kernel threads,
> init and other system daemons or utilities etc., and tenant tasks tagged.
> Then at least two untagged tasks can be scheduled on the same core.
> 
> Kindly let me know if you see a problem with this.

Let me clarify; when the rq->core->core_cookie == 0, each sibling should
schedule independently.

As Julien found, there were some issues here, but the intent was:

  core_cookie 0, independent scheduling
  core_cookie 0->n, core scheduling
  core_cookie n->0, one last core schedule to kick possibly forced idle siblings