From owner-freebsd-hackers Thu Oct 29 15:15:22 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id PAA10245 for freebsd-hackers-outgoing; Thu, 29 Oct 1998 15:15:22 -0800 (PST) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from dingo.cdrom.com (dingo.cdrom.com [204.216.28.145]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id PAA10238 for ; Thu, 29 Oct 1998 15:15:18 -0800 (PST) (envelope-from mike@dingo.cdrom.com) Received: from dingo.cdrom.com (localhost.cdrom.com [127.0.0.1]) by dingo.cdrom.com (8.9.1/8.8.8) with ESMTP id PAA00616; Thu, 29 Oct 1998 15:13:18 -0800 (PST) (envelope-from mike@dingo.cdrom.com) Message-Id: <199810292313.PAA00616@dingo.cdrom.com> X-Mailer: exmh version 2.0.2 2/24/98 To: Shafia Kausar cc: FreeBSD Hackers , shafiak@ee.tamu.edu Subject: Re: Timer Granularity In-reply-to: Your message of "Thu, 29 Oct 1998 12:41:31 CST." Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Thu, 29 Oct 1998 15:13:18 -0800 From: Mike Smith Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > I am new to the FreeBSD OS. I have a few questions for which I could not > find answers on the webpages. > > I am using the FreeBSD version 2.1.5 Relase #2. What is the kernel clock > granularity in this version? 10ms, if I remember correctly. > There are a number of clocks being used in FreeBSD. Which clock is used > for real time kernel processing? Is this accessible to the users? No clocks are "accessible to the users". User applications obtain time values from the system. > Has the timer granularity improved in the releases following this release? Yes. Timer support now offers nanosecond resolution, dependant on the particular clock source(s) in use. > In the /sys/kern/kern_clock.c file the variable time_precision has been > initialised to 1microsec, but it has been stated that the resolution > decreases depending on whether the external clock is working or not. > What is the range of the variation in the resolutuion? It depends on the hardware in use. On some systems the Pentium TSC is available as a time source, in which case time resolution is one CPU cycle. The i8254 timecounter generally has an operating frequency around 1.19MHz, giving a resolution of approximately 1us. -- \\ 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-hackers" in the body of the message