From owner-svn-src-all@FreeBSD.ORG Mon Jun 20 09:06:45 2011 Return-Path: Delivered-To: svn-src-all@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 316DD106564A; Mon, 20 Jun 2011 09:06:45 +0000 (UTC) (envelope-from peterjeremy@acm.org) Received: from mail36.syd.optusnet.com.au (mail36.syd.optusnet.com.au [211.29.133.76]) by mx1.freebsd.org (Postfix) with ESMTP id AC7DE8FC12; Mon, 20 Jun 2011 09:06:44 +0000 (UTC) Received: from server.vk2pj.dyndns.org (c220-239-116-103.belrs4.nsw.optusnet.com.au [220.239.116.103]) by mail36.syd.optusnet.com.au (8.13.1/8.13.1) with ESMTP id p5K96ft2030893 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 20 Jun 2011 19:06:42 +1000 X-Bogosity: Ham, spamicity=0.000000 Received: from server.vk2pj.dyndns.org (localhost.vk2pj.dyndns.org [127.0.0.1]) by server.vk2pj.dyndns.org (8.14.4/8.14.4) with ESMTP id p5K96f6K065239; Mon, 20 Jun 2011 19:06:41 +1000 (EST) (envelope-from peter@server.vk2pj.dyndns.org) Received: (from peter@localhost) by server.vk2pj.dyndns.org (8.14.4/8.14.4/Submit) id p5K96eK4065238; Mon, 20 Jun 2011 19:06:40 +1000 (EST) (envelope-from peter) Date: Mon, 20 Jun 2011 19:06:40 +1000 From: Peter Jeremy To: Bruce Evans Message-ID: <20110620090640.GA64900@server.vk2pj.dyndns.org> References: <201106081938.p58JcWuB044252@svn.freebsd.org> <20110609055112.P2870@besplex.bde.org> <201106081913.09272.jkim@FreeBSD.org> <20110618210815.W889@besplex.bde.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="k1lZvvs/B4yU6o8G" Content-Disposition: inline In-Reply-To: <20110618210815.W889@besplex.bde.org> X-PGP-Key: http://members.optusnet.com.au/peterjeremy/pubkey.asc User-Agent: Mutt/1.5.21 (2010-09-15) Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: svn commit: r222866 - head/sys/x86/x86 X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 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: Mon, 20 Jun 2011 09:06:45 -0000 --k1lZvvs/B4yU6o8G Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2011-Jun-18 22:05:06 +1000, Bruce Evans wrote: >My clock measurement program (mostly an old program by Wollman) shows >the following histogram of times for a non-invariant TSC timecounter >on a 2GHz UP system: > >% min 273, max 265102, mean 273.998217, std 79.069534 >% 1th: 273 (1727219 observations) >% 2th: 274 (265607 observations) >% 3th: 275 (6984 observations) >% 4th: 280 (11 observations) >% 5th: 290 (8 observations) > >The variance is small, and differences of a single nS can be seen clearly. Unfortunately, Intel broke this in their P-state invariant TSC implementation. Rather than incrementing the TSC by one at the CPU core frequency, they increment by the core multiplier at the FSB frequency. This gives a result like the following on my Atom N270: delta samples 24 49637124 36 50312540 48 44658 60 77 This makes it virtually impossible to measure short periods. Luckily, AMD seem to have gotten this right. --=20 Peter Jeremy --k1lZvvs/B4yU6o8G Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.17 (FreeBSD) iEYEARECAAYFAk3/DaAACgkQ/opHv/APuIdI0wCgij6nEhp+ektNaMC7IsxhSFdI skwAoJPNjU5v015VsBvQx07kGtOnw9dI =Ehiz -----END PGP SIGNATURE----- --k1lZvvs/B4yU6o8G--