From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7FC44C64EB0 for ; Mon, 1 Oct 2018 09:15:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 500B82084C for ; Mon, 1 Oct 2018 09:15:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 500B82084C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xmission.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729126AbeJAPwf (ORCPT ); Mon, 1 Oct 2018 11:52:35 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:48251 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728945AbeJAPwe (ORCPT ); Mon, 1 Oct 2018 11:52:34 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out03.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1g6uIr-0003Nx-Pv; Mon, 01 Oct 2018 03:15:45 -0600 Received: from [105.184.227.67] (helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1g6uIq-0003zv-Cz; Mon, 01 Oct 2018 03:15:45 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Thomas Gleixner Cc: Andrey Vagin , Dmitry Safonov , "linux-kernel\@vger.kernel.org" , Dmitry Safonov <0x7f454c46@gmail.com>, Adrian Reber , Andy Lutomirski , Christian Brauner , Cyrill Gorcunov , "H. Peter Anvin" , Ingo Molnar , Jeff Dike , Oleg Nesterov , Pavel Emelianov , Shuah Khan , "containers\@lists.linux-foundation.org" , "criu\@openvz.org" , "linux-api\@vger.kernel.org" , "x86\@kernel.org" , Alexey Dobriyan , "linux-kselftest\@vger.kernel.org" References: <20180919205037.9574-1-dima@arista.com> <874lej6nny.fsf@xmission.com> <20180924205119.GA14833@outlook.office365.com> <874leezh8n.fsf@xmission.com> <20180925014150.GA6302@outlook.office365.com> <87zhw4rwiq.fsf@xmission.com> <87mus1ftb9.fsf@xmission.com> Date: Mon, 01 Oct 2018 11:15:32 +0200 In-Reply-To: (Thomas Gleixner's message of "Fri, 28 Sep 2018 21:32:15 +0200 (CEST)") Message-ID: <877ej2xc23.fsf_-_@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1g6uIq-0003zv-Cz;;;mid=<877ej2xc23.fsf_-_@xmission.com>;;;hst=in02.mta.xmission.com;;;ip=105.184.227.67;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+lpdnsAg3tLJzTn1LCNtd/EXOpsraF/oc= X-SA-Exim-Connect-IP: 105.184.227.67 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Setting monotonic time? X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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