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Date:   Thu, 11 Apr 2019 11:19:10 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Aaron Lu <aaron.lu@linux.alibaba.com>
Cc:     Tim Chen <tim.c.chen@linux.intel.com>, mingo@kernel.org,
        tglx@linutronix.de, pjt@google.com, torvalds@linux-foundation.org,
        linux-kernel@vger.kernel.org, subhra.mazumdar@oracle.com,
        fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com,
        Aubrey Li <aubrey.intel@gmail.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>
Subject: Re: [RFC][PATCH 13/16] sched: Add core wide task selection and
 scheduling.
Message-ID: <20190411091910.GF4038@hirez.programming.kicks-ass.net>
References: <20190218165620.383905466@infradead.org>
 <20190218173514.667598558@infradead.org>
 <20190402064612.GA46500@aaronlu>
 <20190402082812.GJ12232@hirez.programming.kicks-ass.net>
 <20190405145530.GA453@aaronlu>
 <460ce6fb-6a40-4a72-47e8-cf9c7c409bef@linux.intel.com>
 <20190410043633.GA67532@aaronlu>
 <20190410144418.GH2490@worktop.programming.kicks-ass.net>
 <20190411030541.GA99895@aaronlu>
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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