From owner-freebsd-hackers@FreeBSD.ORG Sat Dec 16 20:47:21 2006 Return-Path: X-Original-To: freebsd-hackers@freebsd.org Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 28C1016A505 for ; Sat, 16 Dec 2006 20:47:21 +0000 (UTC) (envelope-from mldodson@houston.rr.com) Received: from ms-smtp-04.texas.rr.com (ms-smtp-04.texas.rr.com [24.93.47.43]) by mx1.FreeBSD.org (Postfix) with ESMTP id 2FACA43CA3 for ; Sat, 16 Dec 2006 20:47:20 +0000 (GMT) (envelope-from mldodson@houston.rr.com) Received: from localhost.houston.rr.com (cpe-24-167-77-130.houston.res.rr.com [24.167.77.130]) by ms-smtp-04.texas.rr.com (8.13.6/8.13.6) with ESMTP id kBGKlHs3017215; Sat, 16 Dec 2006 14:47:17 -0600 (CST) Received: from localhost (localhost [[UNIX: localhost]]) by localhost.houston.rr.com (8.13.8/8.13.6/Submit) id kBGKlCV5083206; Sat, 16 Dec 2006 14:47:12 -0600 (CST) (envelope-from mldodson@houston.rr.com) X-Authentication-Warning: localhost.houston.rr.com: bdodson set sender to mldodson@houston.rr.com using -f From: "M. L. Dodson" To: "M. Warner Losh" Date: Sat, 16 Dec 2006 14:47:12 -0600 User-Agent: KMail/1.9.4 References: <200612141437.28724.mldodson@houston.rr.com> <20061216.113017.-345495563.imp@bsdimp.com> In-Reply-To: <20061216.113017.-345495563.imp@bsdimp.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200612161447.12600.mldodson@houston.rr.com> X-Virus-Scanned: Symantec AntiVirus Scan Engine X-Mailman-Approved-At: Sat, 16 Dec 2006 22:20:18 +0000 Cc: freebsd-hackers@freebsd.org Subject: Re: "Syncing cpus" on a multi-cpu, dual core system X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: mldodson@houston.rr.com List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 16 Dec 2006 20:47:21 -0000 On Saturday 16 December 2006 12:30, M. Warner Losh wrote: > In message: <200612141437.28724.mldodson@houston.rr.com> > > "M. L. Dodson" writes: > : On a computational chemistry list I subscribe to there is a > : current thread about multi-cpu systems needing to have the cpu > : frequencies synced (this is in a Linux context). This is > : evidently not just having the cpus running at nominally the same > : frequency but something else in addition. A posting in the thread > : said variations less than 0.1% were not problematic. However, the > : poster said it was an issue in a dual cpu, dual core system he had > : set up. > : > : My questions are: > : 1. Is this real or an urban legend? > : 2. If real, is this a Linuxism or is FreeBSD affected as well? > : 3. How do you "sync" the cpus, if it is needed? > : 4. anything else some one wants to expound on along this line. > > Linux keeps the cpu's frequencies 'synchronized' so that it can use > the fast time keeping hardware (TSC). FreeBSD uses different > mechanisms for its timekeeping, so doesn't need to keep them in sync > at all, and doesn't even try at this point. Maybe this is what they > are talking about... > > Warner That is very much in line with the context of the postings on the computational chemistry list I mentioned. This is the likely source of the issue for people on that list (very few use *BSD). They just assume if you are not using Solaris or Irix, then you must be using Linux of some flavor. And this means I don't have to bother with that particular piece of nonsense. Thanks to everyone who answered. Bud Dodson -- M. L. Dodson Email: mldodson-at-houston-dot-rr-dot-com Phone: eight_three_two-56_three-386_one