From owner-svn-src-all@freebsd.org Sat Nov 25 16:20:57 2017 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 58854DE8FFC for ; Sat, 25 Nov 2017 16:20:57 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: from mail-it0-x234.google.com (mail-it0-x234.google.com [IPv6:2607:f8b0:4001:c0b::234]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 1EC1B64D0C for ; Sat, 25 Nov 2017 16:20:57 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: by mail-it0-x234.google.com with SMTP id x13so16331311iti.4 for ; Sat, 25 Nov 2017 08:20:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bsdimp-com.20150623.gappssmtp.com; s=20150623; h=mime-version:sender:in-reply-to:references:from:date:message-id :subject:to:cc; bh=5k7wVqDi20T9L4lT1umQEO73TymWS9XvLuWc0t6pcVM=; b=tt8ZeMeVA6lWFzKcFKdfQU/9RteQ7vW/SJAgSAAsbILkh7jhvXhPAE0KQPyOF1wA1k IT3c/4ziLVqIofBUJ8i4yWZTdV+6fGCB+nKLGQCmT/B9A8z1lqTapYQ7zhiUpZs+DAF9 PKy0RP1HPk7KOa2G90QdsrkGOae13Arj59r/y7PN9TBK8JibdGBznMhAv5HvPhoGMDpq cQ6W/tJLSQdjrj/wqhSz09MzF/OwcZ6lZAJH8xHWGe+lEAte2ItAap9Gx8HRzT5En99j jaEpwjO8XsgOy4TUozzRokpkW/uKLwUQS+MRCcqPGkiLUasOzyfwqFY6EEML62kBmvbD HdHQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:sender:in-reply-to:references:from :date:message-id:subject:to:cc; bh=5k7wVqDi20T9L4lT1umQEO73TymWS9XvLuWc0t6pcVM=; b=CwYSf0fc2lW29eHIsNroDjEXwHK3t3rH9bSDnxMw9KtIx0/d9urI+d6hDjd7wDZsl0 Q8wQXAsQX9ggKR7aiQdAhXh0J+2Ngb4I6SnpuBj/Ts4tejEFhIKXU76KBpNneRpG5tdK X8jSBnL067kl7U3yQ9mUpg7m+Vfe4TzvT0ObdpNFhustwC1Hb9HFi6BjBZ6i9NkjCYxa P+L0ju15UGzNUa76/cYYJdT861aROYOgW1pkEmIHsBXoJD8sdX9mm0xlGxb5NQtsDagi 1VjtH3gUsyEidltfu360P28PTWTmvfsJCSNJ/chW/jxMVDM4VwVgymCEO9Ops3DtBWvK SQng== X-Gm-Message-State: AJaThX6sjAIaZaTYA8i2HZzEkj+s4LoyRs+mdr2TMDQFcN5cKOHHiVza QMyYhIs6WNfHAZ5hAJBVnvREHOTCoGz6hu82M8zGBQ== X-Google-Smtp-Source: AGs4zMYZkXjzosNun8AaEb0hVaKMlNn7Jc8p9e46RWjZ1514MT1X72YJiLh4JSrBJqsNnsfUUn+n4v2kXAt73jphA1U= X-Received: by 10.36.131.200 with SMTP id d191mr21097554ite.97.1511626856305; Sat, 25 Nov 2017 08:20:56 -0800 (PST) MIME-Version: 1.0 Sender: wlosh@bsdimp.com Received: by 10.79.108.204 with HTTP; Sat, 25 Nov 2017 08:20:55 -0800 (PST) X-Originating-IP: [2603:300b:6:5100:9579:bb73:7b7f:aadd] In-Reply-To: <20171125201623.J1236@besplex.bde.org> References: <201711231729.vANHTVmo092083@pdx.rh.CN85.dnsmgr.net> <20171124201621.K980@besplex.bde.org> <1511539000.94268.17.camel@freebsd.org> <20171125201623.J1236@besplex.bde.org> From: Warner Losh Date: Sat, 25 Nov 2017 09:20:55 -0700 X-Google-Sender-Auth: fdovqoc00FriV9lR9xAXws6aJ0w Message-ID: Subject: Re: svn commit: r326095 - head/usr.sbin/bsdinstall/scripts To: Bruce Evans Cc: Ian Lepore , Devin Teske , "Rodney W. Grimes" , "Conrad E. Meyer" , Emmanuel Vadot , src-committers , "svn-src-all@freebsd.org" , "svn-src-head@freebsd.org" Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.25 X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 25 Nov 2017 16:20:57 -0000 On Sat, Nov 25, 2017 at 4:09 AM, Bruce Evans wrote: > Is there any use for ntp as a client if you have an atomic clock? Just to > validate both it and ntpd? NTP is a peer to peer time exchange. You run the same daemon either way. However, in the reference clock case, which is what you're talking about, the system still steers its time using ntp. ntp measures the differences between the atomic clock and the system time and adjusts the frequency offset to steer our any frequency error as well as introducing slight frequency errors to steer out any phase difference. gettimeofday() can't ask the atomic clock directly what time it is. So the ntp daemon is doing a time exchange not with a remote clock, but with a local one to get the right time. Some reference clock know the phase and frequency of the time (say a GPS receiver), others just know the frequency (an atomic clock just produces a PPS frequency standard, for example, since the time it's set to isn't from an internal to the clock source of truth). ntpd copes with all these issues to create a "paper clock" that it then steers the system to. Warner