From owner-freebsd-current Sun Sep 6 14:31:30 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id OAA00758 for freebsd-current-outgoing; Sun, 6 Sep 1998 14:31:30 -0700 (PDT) (envelope-from owner-freebsd-current@FreeBSD.ORG) Received: from word.smith.net.au (castles157.castles.com [208.214.165.157]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id OAA00753 for ; Sun, 6 Sep 1998 14:31:27 -0700 (PDT) (envelope-from mike@word.smith.net.au) Received: from word.smith.net.au (LOCALHOST [127.0.0.1]) by word.smith.net.au (8.9.1/8.8.8) with ESMTP id OAA10133; Sun, 6 Sep 1998 14:37:48 -0700 (PDT) (envelope-from mike@word.smith.net.au) Message-Id: <199809062137.OAA10133@word.smith.net.au> X-Mailer: exmh version 2.0.2 2/24/98 To: Thomas Dean cc: current@FreeBSD.ORG Subject: Re: Dmesg Timecounter Varies In-reply-to: Your message of "Sat, 05 Sep 1998 08:14:15 PDT." <199809051514.IAA00899@ix.netcom.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Sun, 06 Sep 1998 14:37:47 -0700 From: Mike Smith Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > I have noticed that the Timecounter value varies greatly in DMESG. > > I am running an SMP kernel. I extracted the values from > /var/log/messages and passed them thru a stat process: > > Timecounter Cost Statistics > Processing /var/log/messages and /var/log/messages.?.gz > > Frequency: 1193182 Hz - Always this value, unless stated. > 1/freq Time: 838 nsec > No. Cycles: 3 - floor( mean/(1/freqTime) ). > Cycle Time: 948 nsec - mean/(no. cycles). > Overhead: 332 nsec - Total overhead in Timecounter cost. > > Entries: 125 - Number of Timecounter entries in messages. > Minimum: 2517 nsec > Maximum: 41603 nsec - Wow! Flyer! > Mean: 2846 nsec > Std. Dev.: 3494.46 > > Notice the maximum flyer. What causes this variability? Unexpected execution discontinuities; most often SMI activity. We are going to have to discontinue our (ab)use of the TSC simply because it's not reliable enough. PC timekeeping *sucks*. -- \\ Sometimes you're ahead, \\ Mike Smith \\ sometimes you're behind. \\ mike@smith.net.au \\ The race is long, and in the \\ msmith@freebsd.org \\ end it's only with yourself. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message