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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Carlos O'Donell <carlos@redhat.com>,
        Zack Weinberg <zackw@panix.com>, Cyril Hrubis <chrubis@suse.cz>
Cc:     Dmitry Safonov <dima@arista.com>, Andrei Vagin <avagin@gmail.com>,
        GNU C Library <libc-alpha@sourceware.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [Y2038][time namespaces] Question regarding CLOCK_REALTIME support plans in Linux time namespaces
In-Reply-To: <7a4d7b14-1f0b-4c40-2bd1-2582d8b71868@redhat.com>
References: <20201030110229.43f0773b@jawa> <20201030135816.GA1790@yuki.lan> <CAKCAbMgemuaG61seKMvhjOHdPCEQJRQBiQgzcf_eO=xm2t+KBw@mail.gmail.com> <87sg9vn40t.fsf@nanos.tec.linutronix.de> <72bbb207-b041-7710-98ad-b08579fe17e4@redhat.com> <87h7qbmqc3.fsf@nanos.tec.linutronix.de> <7bb5837f-1ff6-2b2c-089e-e2441d31ddb2@redhat.com> <87k0v7kwdc.fsf@nanos.tec.linutronix.de> <7a4d7b14-1f0b-4c40-2bd1-2582d8b71868@redhat.com>
Date:   Sat, 07 Nov 2020 01:47:10 +0100
Message-ID: <87y2jej8mp.fsf@nanos.tec.linutronix.de>
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On Thu, Nov 05 2020 at 12:25, Carlos O'Donell wrote:
> On 10/30/20 9:38 PM, Thomas Gleixner wrote:
> If kata grows up quickly perhaps this entire problem becomes solved, but until
> then I continue to have a testing need for a distinct CLOCK_REALTIME in a
> time namespace (and it need not be unconditional, if I have to engage magic
> then I'm happy to do that).

Conditional, that might be a way to go.

Would CONFIG_DEBUG_DISTORTED_CLOCK_REALTIME be a way to go? IOW,
something which is clearly in the debug section of the kernel which wont
get turned on by distros (*cough*) and comes with a description that any
bug reports against it vs. time correctness are going to be ignored.

> * Adding CLOCK_REALTIME to the kernel is a lot of work given the expected
>   guarantees for a local system.

Correct.

> * CLOCK_REALTIME is an expensive resource to maintain, even more expensive
>   than other resources where the kernel can balance their usage.

Correct.

> * On balance it would be better to use vm or vm+containers e.g. kata as a
>   solution to having CLOCK_REALTIME distinct in the container.

That'd be the optimal solution, but the above might be a middle ground.

Thanks,

        tglx