linux-kernel - Re: [RFC PATCH 00/13] Core scheduling v5

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Date:   Mon, 29 Jun 2020 20:33:54 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [RFC PATCH 00/13] Core scheduling v5

Hi Vineeth,

On 2020/6/26 4:12, Vineeth Remanan Pillai wrote:
> On Wed, Mar 4, 2020 at 12:00 PM vpillai <vpillai@...italocean.com> wrote:
>>
>>
>> Fifth iteration of the Core-Scheduling feature.
>>
> Its probably time for an iteration and We are planning to post v6 based
> on this branch:
>  https://github.com/digitalocean/linux-coresched/tree/coresched/pre-v6-v5.7.y
> 
> Just wanted to share the details about v6 here before posting the patch
> series. If there is no objection to the following, we shall be posting
> the v6 early next week.
> 
> The main changes from v6 are the following:
> 1. Address Peter's comments in v5
>    - Code cleanup
>    - Remove fixes related to hotplugging.
>    - Split the patch out for force idling starvation
> 3. Fix for RCU deadlock
> 4. core wide priority comparison minor re-work.
> 5. IRQ Pause patch
> 6. Documentation
>    - https://github.com/digitalocean/linux-coresched/blob/coresched/pre-v6-v5.7.y/Documentation/admin-guide/hw-vuln/core-scheduling.rst
> 
> This version is much leaner compared to v5 due to the removal of hotplug
> support. As a result, dynamic coresched enable/disable on cpus due to
> smt on/off on the core do not function anymore. I tried to reproduce the
> crashes during hotplug, but could not reproduce reliably. The plan is to
> try to reproduce the crashes with v6, and document each corner case for crashes
> as we fix those. Previously, we randomly fixed the issues without a clear
> documentation and the fixes became complex over time.
> 
> TODO lists:
> 
>  - Interface discussions could not come to a conclusion in v5 and hence would
>    like to restart the discussion and reach a consensus on it.
>    - https://lwn.net/ml/linux-kernel/20200520222642.70679-1-joel@joelfernandes.org
> 
>  - Core wide vruntime calculation needs rework:
>    - https://lwn.net/ml/linux-kernel/20200506143506.GH5298@hirez.programming.kicks-ass.net
> 
>  - Load balancing/migration changes ignores group weights:
>    - https://lwn.net/ml/linux-kernel/20200225034438.GA617271@ziqianlu-desktop.localdomain

According to Aaron's response below:
https://lwn.net/ml/linux-kernel/20200305085231.GA12108@ziqianlu-desktop.localdomain/

The following logic seems to be helpful for Aaron's case.

+	/*
+	 * Ignore cookie match if there is a big imbalance between the src rq
+	 * and dst rq.
+	 */
+	if ((src_rq->cfs.h_nr_running - rq->cfs.h_nr_running) > 1)
+		return true;

I didn't see any other comments on the patch at here:
https://lwn.net/ml/linux-kernel/67e46f79-51c2-5b69-71c6-133ec10b68c4@linux.intel.com/

Do we have another way to address this issue?

Thanks,
-Aubrey