Date: Thu, 04 Jun 1998 22:27:52 -0400 From: "Louis A. Mamakos" <louie@TransSys.COM> To: Mark Handley <mjh@east.isi.edu> Cc: Jim Lowe <james@miller.cs.uwm.edu>, multimedia@FreeBSD.ORG Subject: Re: Tick, tock, I need a fast clock... Message-ID: <199806050227.WAA11206@whizzo.transsys.com> In-Reply-To: Your message of "Thu, 04 Jun 1998 14:03:59 EDT." <3710.896983439@north.lcs.mit.edu> References: <3710.896983439@north.lcs.mit.edu>
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> > >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
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