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From:   Don Hiatt <dhiatt@digitalocean.com>
Date:   Wed, 12 May 2021 14:07:31 -0700
Message-ID: <CAOY2Woy-R0WeWN-2ZCwpE2S7Qox41C_PPxmkqN5QHJr7ANhRTQ@mail.gmail.com>
Subject: Re: [PATCH 17/19] sched: Inherit task cookie on fork()
To:     Josh Don <joshdon@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Chris Hyser <chris.hyser@oracle.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Ingo Molnar <mingo@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Mel Gorman <mgorman@suse.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Thomas Glexiner <tglx@linutronix.de>
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On Wed, May 12, 2021 at 1:58 PM Josh Don <joshdon@google.com> wrote:
>
> On Wed, May 12, 2021 at 2:05 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > Right, I need a Champion that actually cares about cgroups and has
> > use-cases to go argue with TJ on this. I've proposed code that I think
> > has sane semantics, but I'm not in a position to argue for it, given I
> > think a world without cgroups is a better world :-)))
>
> Not sure if Tejun has any thoughts on
> http://lkml.kernel.org/r/CABk29NtahuW6UERvRdK5v8My_MfPsoESDKXUjGdvaQcHOJEMvg@mail.gmail.com.
>
> We're looking at using the prctl interface with one of our main
> internal users of core scheduling. As an example, suppose we have a
> management process that wants to make tasks A and B share a cookie:
> - Spawn a new thread m, which then does the following, and exits.
> - PR_SCHED_CORE_CREATE for just its own PID
> - PR_SCHED_CORE_SHARE_TO A
> - PR_SCHED_CORE_SHARE_TO B
>
> That seems to work ok; I'll follow up if there are any pain points
> that aren't easily addressed with the prctl interface.

This is exactly what I'm doing to tag all the processes for qemu. I have as
shell script that creates a cookie for $BASHPID and then SHARE_TO all
the process and it works just great. :)

don