Date: Fri, 3 Nov 2000 10:17:25 -0800 From: Alfred Perlstein <bright@wintelcom.net> To: Zhiui Zhang <zzhang@cs.binghamton.edu> Cc: Poul-Henning Kamp <phk@critter.freebsd.dk>, freebsd-hackers@FreeBSD.ORG Subject: Re: granularity of gettimeofday() Message-ID: <20001103101725.K20567@fw.wintelcom.net> In-Reply-To: <Pine.SOL.4.21.0011031255360.118-100000@jade>; from zzhang@cs.binghamton.edu on Fri, Nov 03, 2000 at 01:01:17PM -0500 References: <920.973271386@critter> <Pine.SOL.4.21.0011031255360.118-100000@jade>
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* Zhiui Zhang <zzhang@cs.binghamton.edu> [001103 10:08] wrote: > > > On Fri, 3 Nov 2000, Poul-Henning Kamp wrote: > > > In message <Pine.SOL.4.21.0011031156050.29568-100000@jade>, Zhiui Zhang writes: > > > > > >The manual says the granularity of gettimeofday() is hardware dependent. > > >The time may be updated continuously or in clock ticks. Can anyone > > >explain for me the two different ways of updating the time? What kind of > > >hardware can help? > > > > You probably need to tell me what you need first... > > This is actually a question from the book "Kernel Project for Linux" and I > am a TA for an operating system course that uses this textbook. I know a > little bit of NTP and Intel Time stamp counter. I need an authoritive > answer for this question because I do not have the time to go through the > FreeBSD code to find out myself in a short time. My impression is that if > the time is updated by an interrupt handler per tick, it can not get a > microsecond granularity. Gettimeofday will force a check of the system hardware, basically you should get better than 100HZ resolution with gettimeofday. -- -Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org] "I have the heart of a child; I keep it in a jar on my desk." To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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