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

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Message-ID: <20191121180555.GA440967@gmail.com>
Date:   Thu, 21 Nov 2019 10:05:55 -0800
From:   Andrei Vagin <avagin@...il.com>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     linux-kernel@...r.kernel.org,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Adrian Reber <adrian@...as.de>,
        Andrei Vagin <avagin@...nvz.org>,
        Andy Lutomirski <luto@...nel.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>, Ingo Molnar <mingo@...hat.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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        containers@...ts.linux-foundation.org, criu@...nvz.org,
        linux-api@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCHv8 00/34] kernel: Introduce Time Namespace

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
>