Date: Thu, 29 Oct 1998 15:13:18 -0800 From: Mike Smith <mike@smith.net.au> To: Shafia Kausar <s0k9955@unix.tamu.edu> Cc: FreeBSD Hackers <freebsd-hackers@FreeBSD.ORG>, shafiak@ee.tamu.edu Subject: Re: Timer Granularity Message-ID: <199810292313.PAA00616@dingo.cdrom.com> In-Reply-To: Your message of "Thu, 29 Oct 1998 12:41:31 CST." <Pine.SOL.3.96.981029123940.26121A-100000@scully.tamu.edu>
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> 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
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