From owner-svn-src-head@freebsd.org Sat Nov 25 16:20:57 2017 Return-Path: Delivered-To: svn-src-head@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 53800DE8FFB for ; Sat, 25 Nov 2017 16:20:57 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: from mail-it0-x230.google.com (mail-it0-x230.google.com [IPv6:2607:f8b0:4001:c0b::230]) (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 1ECC664D0F for ; Sat, 25 Nov 2017 16:20:57 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: by mail-it0-x230.google.com with SMTP id b5so16336259itc.3 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=Gxly0e9c4jBqQl+aylWJojDcIvVt/LxSpLQaM8CZrVcMfzvCWIn94TWATIPbDBoBSh 7agn4WUk9RPCH/AQTxjLerCO2ztuJBepUMY9a8Hv+YfB7hVJOXEpXhGvQ81uSHnvvgQK uLK0EhjrdDuYNYNriYuzWLSkmbA+AEieSqsUIHu359CoxAv30Fr0z7g1cct2rJRdA/Im NqKcmFrSYs49O39mYiXFVM5HaX7gR4pGZdRjXf8sjxP2DgPjH57VfF9GViNHhdnYTLK9 d4xOlyQCUNqp0DEDczMgoOK0kcn6PwzGjuQUsmIbJCApzbpGFxDfA5T5mB5R5Ol9zDfa bvRQ== X-Gm-Message-State: AJaThX7Y15cm9xtoPkaMPgch4oGeFxi6uoG/RER4cc4P/EN0FSKtlPeT AK/S1Vhcn5H0Hn1H7qNc8wwUcTmjSSur6tO5bL+kBA== 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-head@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: SVN commit messages for the src tree for head/-current 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