From: ebiederm at xmission.com (Eric W. Biederman) Subject: Setting monotonic time? Date: Mon, 01 Oct 2018 11:15:32 +0200 [thread overview] Message-ID: <877ej2xc23.fsf_-_@xmission.com> (raw) In-Reply-To: <alpine.DEB.2.21.1809282023350.1432@nanos.tec.linutronix.de> (Thomas Gleixner's message of "Fri, 28 Sep 2018 21:32:15 +0200 (CEST)") 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? 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? Eric
WARNING: multiple messages have this Message-ID (diff)
From: ebiederm@xmission.com (Eric W. Biederman) Subject: Setting monotonic time? Date: Mon, 01 Oct 2018 11:15:32 +0200 [thread overview] Message-ID: <877ej2xc23.fsf_-_@xmission.com> (raw) Message-ID: <20181001091532.RN1YfcbsCOfIIKKf5KyWYmWpgirbozlmrDY87Tw8MS8@z> (raw) In-Reply-To: <alpine.DEB.2.21.1809282023350.1432@nanos.tec.linutronix.de> (Thomas Gleixner's message of "Fri, 28 Sep 2018 21:32:15 +0200 (CEST)") 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? 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? Eric
next prev parent reply other threads:[~2018-10-01 9:15 UTC|newest] Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-09-19 20:50 [RFC 00/20] ns: Introduce Time Namespace dima 2018-09-19 20:50 ` Dmitry Safonov 2018-09-19 20:50 ` [RFC 16/20] selftest: Add Time Namespace test for supported clocks dima 2018-09-19 20:50 ` Dmitry Safonov 2018-09-24 21:36 ` shuah 2018-09-24 21:36 ` Shuah Khan 2018-09-19 20:50 ` [RFC 17/20] selftest/timens: Add test for timerfd dima 2018-09-19 20:50 ` Dmitry Safonov 2018-09-19 20:50 ` [RFC 18/20] selftest/timens: Add test for clock_nanosleep dima 2018-09-19 20:50 ` Dmitry Safonov 2018-09-19 20:50 ` [RFC 19/20] timens/selftest: Add procfs selftest dima 2018-09-19 20:50 ` Dmitry Safonov 2018-09-19 20:50 ` [RFC 20/20] timens/selftest: Add timer offsets test dima 2018-09-19 20:50 ` Dmitry Safonov 2018-09-21 12:27 ` [RFC 00/20] ns: Introduce Time Namespace ebiederm 2018-09-21 12:27 ` Eric W. Biederman 2018-09-24 20:51 ` avagin 2018-09-24 20:51 ` Andrey Vagin 2018-09-24 22:02 ` ebiederm 2018-09-24 22:02 ` Eric W. Biederman 2018-09-25 1:42 ` avagin 2018-09-25 1:42 ` Andrey Vagin 2018-09-26 17:36 ` ebiederm 2018-09-26 17:36 ` Eric W. Biederman 2018-09-26 17:59 ` 0x7f454c46 2018-09-26 17:59 ` Dmitry Safonov 2018-09-27 21:30 ` tglx 2018-09-27 21:30 ` Thomas Gleixner 2018-09-27 21:41 ` tglx 2018-09-27 21:41 ` Thomas Gleixner 2018-10-01 23:20 ` avagin 2018-10-01 23:20 ` Andrey Vagin 2018-10-02 6:15 ` tglx 2018-10-02 6:15 ` Thomas Gleixner 2018-10-02 21:05 ` 0x7f454c46 2018-10-02 21:05 ` Dmitry Safonov 2018-10-02 21:26 ` tglx 2018-10-02 21:26 ` Thomas Gleixner 2018-09-28 17:03 ` ebiederm 2018-09-28 17:03 ` Eric W. Biederman 2018-09-28 19:32 ` tglx 2018-09-28 19:32 ` Thomas Gleixner 2018-10-01 9:05 ` ebiederm 2018-10-01 9:05 ` Eric W. Biederman 2018-10-01 9:15 ` ebiederm [this message] 2018-10-01 9:15 ` Setting monotonic time? Eric W. Biederman 2018-10-01 18:52 ` tglx 2018-10-01 18:52 ` Thomas Gleixner 2018-10-02 20:00 ` arnd 2018-10-02 20:00 ` Arnd Bergmann 2018-10-02 20:06 ` tglx 2018-10-02 20:06 ` Thomas Gleixner 2018-10-03 4:50 ` ebiederm 2018-10-03 4:50 ` Eric W. Biederman 2018-10-03 5:25 ` tglx 2018-10-03 5:25 ` Thomas Gleixner 2018-10-03 6:14 ` ebiederm 2018-10-03 6:14 ` Eric W. Biederman 2018-10-03 7:02 ` arnd 2018-10-03 7:02 ` Arnd Bergmann 2018-10-03 6:14 ` tglx 2018-10-03 6:14 ` Thomas Gleixner 2018-10-01 20:51 ` avagin 2018-10-01 20:51 ` Andrey Vagin 2018-10-02 6:16 ` tglx 2018-10-02 6:16 ` Thomas Gleixner 2018-10-21 1:41 ` [RFC 00/20] ns: Introduce Time Namespace avagin 2018-10-21 1:41 ` Andrei Vagin 2018-10-21 3:54 ` avagin 2018-10-21 3:54 ` Andrei Vagin 2018-10-29 20:33 ` tglx 2018-10-29 20:33 ` Thomas Gleixner 2018-10-29 21:21 ` ebiederm 2018-10-29 21:21 ` Eric W. Biederman 2018-10-29 21:36 ` tglx 2018-10-29 21:36 ` Thomas Gleixner 2018-10-31 16:26 ` avagin 2018-10-31 16:26 ` Andrei Vagin
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