linux-kernel - Re: [PATCHv8 00/34] kernel: Introduce Time Namespace

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Date:   Wed, 11 Dec 2019 20:38:30 +0000
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Dmitry Safonov <dima@...sta.com>, Andrei Vagin <avagin@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        Adrian Reber <adrian@...as.de>,
        Andrei Vagin <avagin@...nvz.org>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>, Jann Horn <jannh@...gle.com>,
        Jeff Dike <jdike@...toit.com>, Oleg Nesterov <oleg@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        crml <criu@...nvz.org>, Linux API <linux-api@...r.kernel.org>,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCHv8 00/34] kernel: Introduce Time Namespace

Gentle ping, in case you have time to look at this.

On Thu, 21 Nov 2019 at 18:05, Andrei Vagin <avagin@...il.com> wrote:
>
> Hi Thomas,
>
> What is your plan on this series? We know you are probably busy with
> the next merge window. We just want to check that this is still in your
> TODO list.
>
> On Tue, Nov 12, 2019 at 01:26:49AM +0000, Dmitry Safonov wrote:
> >
> > v7..v8 Changes:
> > * Fix compile-time errors:
> >   - on architectures without the support of time namespaces.
> >   - when CONFIG_POSIX_TIMERS isn't set.
> > * Added checks in selftests for CONFIG_POSIX_TIMERS.
> > * Inline do_hres and do_coarse.
> >   (And added Tested-by Vincenzo - thanks!)
> > * Make TIME_NS depends on GENERIC_VDSO_TIME_NS and set it per-arch.
> >
> > [v1..v7 Changelogs is at the very bottom here]
> >
> > Our performance measurements show that the price of VDSO's clock_gettime()
> > in a child time namespace is about 8% with a hot CPU cache and about 90%
>
> Here is a typo. The price of VDSO's clock_gettime() in a child time
> namespace is about 12% with a cold CPU cache. The table with
> measurements for a cold CPU cache contains correct data.
>
> > with a cold CPU cache. There is no performance regression for host
> > processes outside time namespace on those tests.
> >
>
> ....
>
> >
> > Cold CPU cache (lesser tsc per cycle - the better):
> >
> >            | before    | CONFIG_TIME_NS=n | host      | inside timens
> > --------------------------------------------------------------
> > tsc        | 476       | 480              | 487       | 531
> > stdev(tsc) | 0.6       | 1.3              | 4.3       | 5.7
> > diff (%)   | 100       | 100.9            | 102       | 112
> >

Thanks,
             Dmitry