Date: Fri, 27 Feb 1998 17:13:34 +0100 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: dannyman <dannyman@sasquatch.dannyland.org> Cc: freebsd-current@FreeBSD.ORG Subject: Re: Curious: "Timecounter"? Message-ID: <3448.888596014@critter.freebsd.dk> In-Reply-To: Your message of "Fri, 27 Feb 1998 09:51:15 CST." <19980227095115.05314@urh.uiuc.edu>
next in thread | previous in thread | raw e-mail | index | archive | help
In message <19980227095115.05314@urh.uiuc.edu>, dannyman writes: >arh0300 kernel log messages: >> Timecounter "i8254" frequency 1193182 Hz cost 2524 ns >> Timecounter "TSC" frequency 99952423 Hz cost 356 ns >> wcd0: 0Kb/sec, caddy >> wcd0: medium type unknown > >Wow, the new kernel compiling mechanism is kinda neat. > >I'm curious about these Timecounter lines. Can anyone explain, in terms a >fairly unsophisticated guy like me could understand, what these lines mean? It means that the machine has two pieces of hardware it can use for the construction of "time-of-day". "frequency" should be pretty obvious, "cost" is how long time it takes to read the counter, and consequently a measure of the overhead by using that timecounter. To get from the reading of the timecounters which is just a binary counter running at "frequency" to microtime() and/or nanotime() various scaled integer math is done. You can find the relevant code in sys/sys/time.h, sys/kern/kern_clock.c, sys/kern/kern_ntptime.c, sys/i386/isa/clock.c -- Poul-Henning Kamp FreeBSD coreteam member phk@FreeBSD.ORG "Real hackers run -current on their laptop." "Drink MONO-tonic, it goes down but it will NEVER come back up!" To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3448.888596014>