linux-api.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Andrey Vagin <avagin@virtuozzo.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	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 Dobriyan <ad>
Subject: Re: Setting monotonic time?
Date: Mon, 1 Oct 2018 20:51:36 +0000	[thread overview]
Message-ID: <20181001205124.GA23620@outlook.office365.com> (raw)
In-Reply-To: <877ej2xc23.fsf_-_@xmission.com>

On Mon, Oct 01, 2018 at 11:15:32AM +0200, Eric W. Biederman wrote:
> 
> In the context of process migration there is a simpler subproblem that I
> think it is worth exploring if we can do something about.
> 
> For a cluster of machines all running with synchronized
> clocks. CLOCK_REALTIME matches. CLOCK_MONOTNIC does not match between
> machines.   Not having a matching CLOCK_MONOTONIC prevents successful
> process migration between nodes in that cluster.
> 
> Would it be possible to allow setting CLOCK_MONOTONIC at the very
> beginning of time?  So that all of the nodes in a cluster can be in
> sync?

Here is a question about how to synchronize clocks between nodes. It
looks like we will need to have a working network for this, but a
network configuration may be non-trivial and it can require to run a few
processes which can use CLOCK_MONOTNIC...

> 
> No change in skew just in offset for CLOCK_MONOTONIC.
> 
> There are also dragons involved in coordinating things so that
> CLOCK_MONOTONIC gets set before CLOCK_MONOTONIC gets used.  So I don't
> know if allowing CLOCK_MONOTONIC to be set would be practical but it
> seems work exploring all on it's own.
> 
> Dmitry would setting CLOCK_MONOTONIC exactly once at boot time solve
> your problem that is you are looking at a time namespace to solve?

Process migration is only one of use-cases. Another use-case is
restoring from snapshots. It may be even more popular than process
migration. We can't guarantee that all snapshots will be done in one
cluster. For example, a user meets a bug, does a container snapshot and
attaches it to a bug report.

> 
> Eric

  parent reply	other threads:[~2018-10-01 20:51 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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20181001205124.GA23620@outlook.office365.com \
    --to=avagin@virtuozzo.com \
    --cc=0x7f454c46@gmail.com \
    --cc=adrian@lisas.de \
    --cc=christian.brauner@ubuntu.com \
    --cc=containers@lists.linux-foundation.org \
    --cc=criu@openvz.org \
    --cc=dima@arista.com \
    --cc=ebiederm@xmission.com \
    --cc=gorcunov@openvz.org \
    --cc=hpa@zytor.com \
    --cc=jdike@addtoit.com \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=mingo@redhat.com \
    --cc=oleg@redhat.com \
    --cc=shuah@kernel.org \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    --cc=xemul@virtuozzo.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).