linux-kernel - Re: [PATCH 0/9] sched: Core scheduling interfaces

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Message-ID: <CABk29NtahuW6UERvRdK5v8My_MfPsoESDKXUjGdvaQcHOJEMvg@mail.gmail.com>
Date:   Mon, 19 Apr 2021 18:17:34 -0700
From:   Josh Don <joshdon@...gle.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Michal Koutný <mkoutny@...e.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        "Hyser,Chris" <chris.hyser@...cle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...e.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Zefan Li <lizefan.x@...edance.com>
Subject: Re: [PATCH 0/9] sched: Core scheduling interfaces

On Mon, Apr 19, 2021 at 2:01 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> Josh, you being on the other Google team, the one that actually uses the
> cgroup interface AFAIU, can you fight the good fight with TJ on this?

A bit of extra context is in
https://lore.kernel.org/lkml/CABk29NtTScu2HO7V9Di+Fh2gv8zu5xiC5iNRwPFCLhpD+DKP0A@mail.gmail.com.

On the management/auditing side, the cgroup interface gives a clear
indication of which tasks share a cookie. It is a bit less attractive
to add a prctl interface for enumerating this.

Also on the management side, I illustrated in the above message how a
thread would potentially group together other threads. One limitation
of the current prctl interface is that the share_{to, from} always
operates on the current thread. Granted we can work around this as
described, and also potentially extend the prctl interface to operate
on two tasks.

So I agree that the cgroup interface here isn't strictly necessary,
though it seems convenient. I will double-check with internal teams
that would be using the interface to see if there are any other
considerations I'm missing.

On Mon, Apr 19, 2021 at 4:30 AM Tejun Heo <tj@...nel.org> wrote:
>
> My suggestion is going ahead with the per-process interface with cgroup
> extension on mind in case actual use cases arise. Also, when planning cgroup
> integration, putting dynamic migration front and center likely isn't a good
> idea.

tasks would not be frequently moved around; I'd expect security
configuration to remain mostly static. Or maybe I'm misunderstanding
your emphasis here?

If you feel the above is not strong enough (ie. there should be a use
case not feasible with prctl), I'd support that we move forward with
the prctl stuff for now, since the cgroup interface is independant.

Thanks,
Josh