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From: Thomas Gleixner <tglx@linutronix.de>
To: Andrey Vagin <avagin@virtuozzo.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	Dmitry Safonov <dima@arista.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Dmitry Safonov <0x7f454c46@gmail.com>,
	Adrian Reber <adrian@lisas.de>, Andy Lutomirski <luto@kernel.org>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Cyrill Gorcunov <gorcunov@openvz.org>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Jeff Dike <jdike@addtoit.com>, Oleg Nesterov <oleg@redhat.com>,
	Pavel Emelianov <xemul@virtuozzo.com>,
	Shuah Khan <shuah@kernel.org>,
	"containers@lists.linux-foundation.org"
	<containers@lists.linux-foundation.org>,
	"criu@openvz.org" <criu@openvz.org>,
	"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	Alexey
Subject: Re: [RFC 00/20] ns: Introduce Time Namespace
Date: Tue, 2 Oct 2018 08:15:15 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1810020811290.32062@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20181001232033.GA31324@outlook.office365.com>

On Mon, 1 Oct 2018, Andrey Vagin wrote:

> On Thu, Sep 27, 2018 at 11:41:49PM +0200, Thomas Gleixner wrote:
> > On Thu, 27 Sep 2018, Thomas Gleixner wrote:
> > > Add time skew via NTP/PTP into the picture and you might have to adjust
> > > timers as well, because you need to guarantee that they are not expiring
> > > early.
> > > 
> > > I haven't looked through Dimitry's patches yet, but I don't see how this
> > > can work at all without introducing subtle issues all over the place.
> > 
> > And just a quick scan tells me that this is broken. Timers will expire
> > early or late. The latter is acceptible to some extent, but larger delays
> > might come with surprise. Expiring early is an absolute nono.
> 
> Do you mean that we have to adjust all timers after changing offset for
> CLOCK_MONOTONIC or CLOCK_BOOTTIME? Our idea is that offsets for
> monotonic and boot times will be set immediately after creating a time
> namespace before using any timers.

I explained that in detail in this thread, but it's not about the initial
setting of clock mono/boot before any timers have been armed.

It's about setting the offset or clock realtime (via settimeofday) when
timers are already armed. Also having a entirely different time domain,
e.g. separate NTP adjustments, makes that necessary.

Thanks,

	tglx

  reply	other threads:[~2018-10-02  6:15 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-19 20:50 [RFC 00/20] ns: Introduce Time Namespace Dmitry Safonov
2018-09-19 20:50 ` [RFC 01/20] " Dmitry Safonov
2018-09-28 18:20   ` Laurent Vivier
2018-09-19 20:50 ` [RFC 02/20] timens: Add timens_offsets Dmitry Safonov
2018-09-20 18:45   ` Cyrill Gorcunov
2018-09-20 22:14     ` Cyrill Gorcunov
2018-09-19 20:50 ` [RFC 03/20] timens: Introduce CLOCK_MONOTONIC offsets Dmitry Safonov
2018-09-19 20:50 ` [RFC 04/20] timens: Introduce CLOCK_BOOTTIME offset Dmitry Safonov
2018-09-30  3:18   ` [LKP] [timens] 3cc8de9dcb: RIP:posix_get_boottime kernel test robot
2018-09-19 20:50 ` [RFC 05/20] timerfd/timens: Take into account ns clock offsets Dmitry Safonov
2018-09-19 20:50 ` [RFC 06/20] kernel: Take into account timens clock offsets in clock_nanosleep Dmitry Safonov
2018-09-19 20:50 ` [RFC 07/20] timens: Shift /proc/uptime Dmitry Safonov
2018-09-19 20:50 ` [RFC 08/20] x86/vdso: Restrict splitting vvar vma Dmitry Safonov
2018-09-19 20:50 ` [RFC 09/20] x86/vdso/timens: Add offsets page in vvar Dmitry Safonov
2018-09-19 20:50 ` [RFC 10/20] x86/vdso: Use set_normalized_timespec() to avoid 32 bit overflow Dmitry Safonov
2018-09-19 20:50 ` [RFC 11/20] x86/vdso: Purge timens page on setns()/unshare()/clone() Dmitry Safonov
2018-09-19 20:50 ` [RFC 12/20] x86/vdso: Look for vvar vma to purge timens page Dmitry Safonov
2018-09-19 20:50 ` [RFC 13/20] posix-timers/timens: Take into account clock offsets Dmitry Safonov
2018-09-30  3:11   ` [LKP] [posix] 25217c6e39: BUG:KASAN:null-ptr-deref_in_c kernel test robot
2018-09-19 20:50 ` [RFC 14/20] timens: Add align for timens_offsets Dmitry Safonov
2018-09-19 20:50 ` [RFC 15/20] timens: Optimize zero-offsets Dmitry Safonov
2018-09-19 20:50 ` [RFC 16/20] selftest: Add Time Namespace test for supported clocks Dmitry Safonov
2018-09-24 21:36   ` Shuah Khan
2018-09-19 20:50 ` [RFC 17/20] selftest/timens: Add test for timerfd Dmitry Safonov
2018-09-19 20:50 ` [RFC 18/20] selftest/timens: Add test for clock_nanosleep Dmitry Safonov
2018-09-19 20:50 ` [RFC 19/20] timens/selftest: Add procfs selftest Dmitry Safonov
2018-09-19 20:50 ` [RFC 20/20] timens/selftest: Add timer offsets test Dmitry Safonov
2018-09-21 12:27 ` [RFC 00/20] ns: Introduce Time Namespace Eric W. Biederman
2018-09-24 20:51   ` Andrey Vagin
2018-09-24 22:02     ` Eric W. Biederman
2018-09-25  1:42       ` Andrey Vagin
2018-09-26 17:36         ` Eric W. Biederman
2018-09-26 17:59           ` Dmitry Safonov
2018-09-27 21:30           ` Thomas Gleixner
2018-09-27 21:41             ` Thomas Gleixner
2018-10-01 23:20               ` Andrey Vagin
2018-10-02  6:15                 ` Thomas Gleixner [this message]
2018-10-02 21:05                   ` Dmitry Safonov
2018-10-02 21:26                     ` Thomas Gleixner
2018-09-28 17:03             ` Eric W. Biederman
2018-09-28 19:32               ` Thomas Gleixner
2018-10-01  9:05                 ` Eric W. Biederman
2018-10-01  9:15                 ` Setting monotonic time? Eric W. Biederman
2018-10-01 18:52                   ` Thomas Gleixner
2018-10-02 20:00                     ` Arnd Bergmann
2018-10-02 20:06                       ` Thomas Gleixner
2018-10-03  4:50                         ` Eric W. Biederman
2018-10-03  5:25                           ` Thomas Gleixner
2018-10-03  6:14                             ` Eric W. Biederman
2018-10-03  7:02                               ` Arnd Bergmann
2018-10-03  6:14                             ` Thomas Gleixner
2018-10-01 20:51                   ` Andrey Vagin
2018-10-02  6:16                     ` Thomas Gleixner
2018-10-21  1:41               ` [RFC 00/20] ns: Introduce Time Namespace Andrei Vagin
2018-10-21  3:54                 ` Andrei Vagin
2018-10-29 20:33                 ` Thomas Gleixner
2018-10-29 21:21                   ` Eric W. Biederman
2018-10-29 21:36                     ` Thomas Gleixner
2018-10-31 16:26                   ` Andrei Vagin

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