From owner-freebsd-current Fri Aug 23 14:14:15 2002 Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id B373437B400 for ; Fri, 23 Aug 2002 14:14:13 -0700 (PDT) Received: from wall.polstra.com (wall-gw.polstra.com [206.213.73.130]) by mx1.FreeBSD.org (Postfix) with ESMTP id 06FAF43E77 for ; Fri, 23 Aug 2002 14:14:13 -0700 (PDT) (envelope-from jdp@polstra.com) Received: from vashon.polstra.com (vashon.polstra.com [206.213.73.13]) by wall.polstra.com (8.11.3/8.11.3) with ESMTP id g7NLE8f24587; Fri, 23 Aug 2002 14:14:08 -0700 (PDT) (envelope-from jdp@vashon.polstra.com) Received: (from jdp@localhost) by vashon.polstra.com (8.12.4/8.12.4/Submit) id g7NLE80E087984; Fri, 23 Aug 2002 14:14:08 -0700 (PDT) (envelope-from jdp) Date: Fri, 23 Aug 2002 14:14:08 -0700 (PDT) Message-Id: <200208232114.g7NLE80E087984@vashon.polstra.com> To: current@freebsd.org From: John Polstra Cc: phk@critter.freebsd.dk Subject: Re: how to compute the skew between TSC in SMP systems ? In-Reply-To: <29486.1030136549@critter.freebsd.dk> References: <29486.1030136549@critter.freebsd.dk> Organization: Polstra & Co., Seattle, WA Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In article <29486.1030136549@critter.freebsd.dk>, Poul-Henning Kamp wrote: > In message <20020823134410.A81962@iguana.icir.org>, Luigi Rizzo writes: > >does anyone have an idea on how to determine the skew between > >TSC content in the various processors on an SMP box ? > > On i386: It cannot be reliably done. Been there, tried that. Well ... you can come pretty close. The BSD/OS kernel has code (conditioned on option SMP_DEBUG) that manages to sync up all TSCs in an N-CPU system such that the measured difference between the extremes is less than 100 counts. John -- John Polstra John D. Polstra & Co., Inc. Seattle, Washington USA "Disappointment is a good sign of basic intelligence." -- Chögyam Trungpa To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message