From owner-freebsd-cloud@freebsd.org Mon Mar 27 00:00:18 2017 Return-Path: Delivered-To: freebsd-cloud@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 D7B3ED1F94F for ; Mon, 27 Mar 2017 00:00:18 +0000 (UTC) (envelope-from newt0311@gmail.com) Received: from mail-ot0-x22f.google.com (mail-ot0-x22f.google.com [IPv6:2607:f8b0:4003:c0f::22f]) (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 9404A13DC for ; Mon, 27 Mar 2017 00:00:18 +0000 (UTC) (envelope-from newt0311@gmail.com) Received: by mail-ot0-x22f.google.com with SMTP id y88so20676068ota.2 for ; Sun, 26 Mar 2017 17:00:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=0hzlABQ91Yb2Npa+fxTNhxMFp4/2fqjPEn/U3uyV5oU=; b=SF78N7U9xRJVEzFMMUBDsgwQD5ysx7IcaoShqY3F/hAOZdQcoaVwqOMEEP/1dEIWiD sNOX+dil67BAAu3MN/Gz7uzckykiTaTpanlShKgVvT5VpeA8/y6ytZQZowuWzzRCt13m s4+6+31xPpn5a5R2QqT2kT10wXquu0xITatEi1XmK9O79BBPTI0iAcIHt7eiTjqMoYE8 mR10JW09QVo97PfnedL6uhP6Kx10VS7o6JLXEYG4/meoQH/uD3/mogG/MnYQghyx2c7e jMEHu/D0BKTCqBNI146z2wxcEJ4MO1SZXdcdBfb3Kuw0PfpNtpvbQaHQzP3htcOWEI+M UPow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=0hzlABQ91Yb2Npa+fxTNhxMFp4/2fqjPEn/U3uyV5oU=; b=W7qyw5qiY3NXGDY2mf36Oj+loLl1ufa6ycCSRFtFMLLFh1fYPJR35bDisz4dE8fKbv z+uyIFCEmGmdSL+zVVVH+iTBJcX/ucXEo3MdoGs/7fBUpwzMqHYSPn90L/G8d2CuvaoF Z7pSDywlnToaVHhb/aWsnQptSez7d2+S1Q8Gp5iMtb2Kqm1be4kNJN85BFmJpx8SmirZ GBVOyBm6Qf4wEPOtgObu5dsGv6tA8MZVhlmlBi2zQ/AtznnKGP51117Y+kwEc9T9tEB8 5qSnvjpSYG4P86mEDeuYXzlfHrHPRqWqM6+pR4hADbYRUmw2Cnxeko6bGSz7SLxPXxY0 vfxA== X-Gm-Message-State: AFeK/H34ZWzDcSms8O0p6SfY1iChbMjZHo7c63Qn19mg+VsHiqiTrW3alaC6o9N+lAXEG3KT9bURJKi8h4EyZw== X-Received: by 10.157.88.29 with SMTP id r29mr4041239oth.68.1490572817778; Sun, 26 Mar 2017 17:00:17 -0700 (PDT) MIME-Version: 1.0 Received: by 10.157.22.217 with HTTP; Sun, 26 Mar 2017 16:59:57 -0700 (PDT) In-Reply-To: References: <0100015b075efd74-2a227e8b-7fc9-4ebb-9187-f549733c1b6c-000000@email.amazonses.com> From: Prakhar Goel Date: Sun, 26 Mar 2017 19:59:57 -0400 Message-ID: Subject: Re: Issues with clock skew on GCE To: Colin Percival Cc: freebsd-cloud@freebsd.org Content-Type: text/plain; charset=UTF-8 X-BeenThere: freebsd-cloud@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "FreeBSD on cloud platforms \(EC2, GCE, Azure, etc.\)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 27 Mar 2017 00:00:19 -0000 Just to close this issue out: The solution I went with was to switch the kernel timecounter to ACPI-fast. I ran a check on this* and whatever the drift, it was small enough for the ntpd process to keep the system clock sync'd (drift less than 0.001s after a day). As a control, I ran the same test on a VM using the TSC (default) timecounter and that machine drifted by ~50 seconds every five minutes (!). Thanks for your help Colin and Bruce. * Just calling ntpdate every five minutes and logging the results. The specific command I used was ntpdate -q metadata.google.internal so it didn't actually update the system clock, just checked the drift against the Google time-servers. -- ________________________ Warm Regards Prakhar Goel