From owner-freebsd-multimedia Thu Jun 4 19:28:41 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id TAA07491 for freebsd-multimedia-outgoing; Thu, 4 Jun 1998 19:28:41 -0700 (PDT) (envelope-from owner-freebsd-multimedia@FreeBSD.ORG) Received: from whizzo.transsys.com (whizzo.TransSys.COM [144.202.42.10]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id TAA07442 for ; Thu, 4 Jun 1998 19:28:00 -0700 (PDT) (envelope-from louie@whizzo.transsys.com) Received: from whizzo.transsys.com (localhost.transsys.com [127.0.0.1]) by whizzo.transsys.com (8.8.8/8.7.3) with ESMTP id WAA11206; Thu, 4 Jun 1998 22:27:53 -0400 (EDT) Message-Id: <199806050227.WAA11206@whizzo.transsys.com> X-Mailer: exmh version 2.0.1 12/23/97 To: Mark Handley cc: Jim Lowe , multimedia@FreeBSD.ORG From: "Louis A. Mamakos" Subject: Re: Tick, tock, I need a fast clock... References: <3710.896983439@north.lcs.mit.edu> In-reply-to: Your message of "Thu, 04 Jun 1998 14:03:59 EDT." <3710.896983439@north.lcs.mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Thu, 04 Jun 1998 22:27:52 -0400 Sender: owner-freebsd-multimedia@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org > > >Are there any timers available to applications in FreeBSD faster than > >10ms? If not, is there a simple way to increase the interval timers > >minimal time to something like .1ms without adversely effecting system > >performance? > > I has the same requirement earlier this week. You can change the > value of HZ in /usr/src/sys/conf/param.c from the default value of 100 > to something larger and rebuild. My system is currently running with > this set to 1000, which allows interval timers using select of around > 2ms (why isn't it 1ms??). The system seems to run fine, but the > values measured for per-process CPU utilization by top (and presumably > other utilities) are low by an order of magnitude. Presumably this is > a bug in some of the kernel stats code. > > It does seem somewhat rediculous that HZ is still set to 100 by > default in these days of 400MHz processors. What's needed is some smarter hardware, not more frequent interrupts. For an example, take a look at http://www.bancomm.com/cbc637PCI.htm for a board with the ability to provide time with approximately microsecond precision. Hook it to an external IRIG-B timecode source, internal GPS receiver for more precise time and frequency. I'm working on a project with the CompactPCI version of this for precise packet arrival timestamps. (e.g., timestamp each packet deep in the driver as it arrives. Just a few PCI bus cycles to do so..) louie To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-multimedia" in the body of the message