linux-kernel - [RFC] Core Scheduling unnecessary force idle?

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Date:   Wed, 29 Nov 2023 16:53:35 +0800
From:   Benjamin Tang <tangsong8264@...il.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org,
        Benjamin Tang <tangsong8264@...il.com>
Subject: [RFC] Core Scheduling unnecessary force idle?

When I'm reading the code related to "core scheduling", I have a question.

Say the RQs in a particular core look like this:
Let CFS1 and CFS4 be 2 untagged CFS tasks.
Let CFS2 and CFS3 be 2 untagged CFS tasks.

          rq0                      rq1
     CFS1(no tag)     CFS3(tagged)
     CFS2(tagged)    CFS4(no tag)

Say schedule() runs on rq0. In the core-wide pick logic, if I'm not 
mistaken,
the end result of the selection will be (say prio(CFS1) > prio(CFS3)):

          rq0                 rq1
     CFS1(no tag)    IDLE

Why not consider trying to find untagged tasks for rq1 here?
Is it because it seems less fair, or are there other considerations?

I would be very grateful if someone could give me some suggestions.
Thanks!

Best Wishes