From owner-freebsd-current Fri Aug 23 14:25: 9 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 26C2437B43A for ; Fri, 23 Aug 2002 14:25:00 -0700 (PDT) Received: from critter.freebsd.dk (critter.freebsd.dk [212.242.86.163]) by mx1.FreeBSD.org (Postfix) with ESMTP id 5645543E65 for ; Fri, 23 Aug 2002 14:24:59 -0700 (PDT) (envelope-from phk@critter.freebsd.dk) Received: from critter.freebsd.dk (localhost [127.0.0.1]) by critter.freebsd.dk (8.12.3/8.12.2) with ESMTP id g7NLLYoc030294; Fri, 23 Aug 2002 23:21:34 +0200 (CEST) (envelope-from phk@critter.freebsd.dk) To: John Polstra Cc: current@freebsd.org Subject: Re: how to compute the skew between TSC in SMP systems ? In-Reply-To: Your message of "Fri, 23 Aug 2002 14:14:08 PDT." <200208232114.g7NLE80E087984@vashon.polstra.com> Date: Fri, 23 Aug 2002 23:21:33 +0200 Message-ID: <30293.1030137693@critter.freebsd.dk> From: Poul-Henning Kamp 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 message <200208232114.g7NLE80E087984@vashon.polstra.com>, John Polstra write s: >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. Was this before or after APM, ACPI, SpeedStep and all the other crap ruined the TSC as a timecounting device ? -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message