linux-kernel - Re: [PATCH 2/6] sched: tagging interface for core scheduling

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Date:   Mon, 22 Mar 2021 14:35:46 -0400
From:   Chris Hyser <chris.hyser@...cle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        torvalds@...ux-foundation.org, fweisbec@...il.com,
        keescook@...omium.org, Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>, vineeth@...byteword.org,
        Chen Yu <yu.c.chen@...el.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Agata Gruza <agata.gruza@...el.com>,
        Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
        graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com,
        rostedt@...dmis.org, benbjiang@...cent.com,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        James.Bottomley@...senpartnership.com, OWeisse@...ch.edu,
        Dhaval Giani <dhaval.giani@...cle.com>,
        Josh Don <joshdon@...gle.com>, Hao Luo <haoluo@...gle.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH 2/6] sched: tagging interface for core scheduling



On 3/22/21 2:33 PM, Peter Zijlstra wrote:
> On Mon, Mar 22, 2021 at 01:57:48PM -0400, Chris Hyser wrote:
>> On 3/20/21 11:46 AM, Peter Zijlstra wrote:
>>> On Fri, Mar 19, 2021 at 04:32:49PM -0400, Joel Fernandes (Google) wrote:
>>>> From: Josh Don <joshdon@...gle.com>
>>>>
>>>> Adds per-task and per-cgroup interfaces for specifying which tasks can
>>>> co-execute on adjacent SMT hyperthreads via core scheduling.
>>>>
>>>> The per-task interface hooks are implemented here, but are not currently
>>>> used. The following patch adds a prctl interface which then takes
>>>> advantage of these.
>>>>
>>>> The cgroup interface can be used to toggle a unique cookie value for all
>>>> descendent tasks, preventing these tasks from sharing with any others.
>>>> See Documentation/admin-guide/hw-vuln/core-scheduling.rst for a full
>>>> rundown.
>>>>
>>>> One important property of this interface is that neither the per-task
>>>> nor the per-cgroup setting overrides the other. For example, if two
>>>> tasks are in different cgroups, and one or both of the cgroups is tagged
>>>> using the per-cgroup interface, then these tasks cannot share, even if
>>>> they use the per-task interface to attempt to share with one another.
>>>>
>>>> The above is implemented by making the overall core scheduling cookie a
>>>> compound structure, containing both a task-level cookie and a
>>>> group-level cookie. Two tasks will only be allowed to share if all
>>>> fields of their respective cookies match.
>>>>
>>>> Core scheduler has extra overhead.  Enable it only for machines with
>>>> more than one SMT hardware thread.
>>>
>>> Oh man.. I'd soooo hoped to first see the simple task interface and then
>>> see the cgroup patch on top of that... I'll see if I can flip them
>>> myself (on monday).
>>
>> Peter, given we need to rebase this and we have some cleanup, we can go
>> ahead and flip the order if you have not yet done so yet.
> 
> I didn't get around to it yet :/ So yes, please! Also can you then split
> the selftest thingies?

Will do.

-chrish