Date: Fri, 21 Jan 2005 13:44:37 +0200 From: Alin-Adrian Anton <aanton@spintech.ro> To: freebsd-hackers@freebsd.org Subject: Re: clock time in milliseconds into a c program Message-ID: <41F0EB25.5030404@spintech.ro> In-Reply-To: <c2d45d6e050121015876defa22@mail.gmail.com> References: <20050120004406.GF921@einstein.lab> <41EFBEA5.50007@spintech.ro> <84dead72050120181965c70231@mail.gmail.com> <c2d45d6e050121015876defa22@mail.gmail.com>
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Claudiu Dragalina-Paraipan wrote: > Or you can use PERFMON. Check manual page for perfmon. > It gives you access to internal counters of CPU. > > Of course this is a subjective measurement, since, AFAIK, the counters > are not kept separately for every process, but for entire system, > including kernel. > Maybe repeating the same measurement for many times, with a system > running no other CPU consumers, you will get a more accurate > measurement > As I said, multiple measurements provide better accuracy. Much better. And as Joseph Koshy pointed out, the RDTSC instruction (works on Pentium i think) may even provide better accuracy then just measuring time. Using it in a cycle of measurements would provide relevant output, and perhaps more accurate then PERFMON (because of direct CPU access). clock_gettime also provides nanoseconds resolution, as pointed out. -- Alin-Adrian Anton GPG keyID 0x1E2FFF2E (2963 0C11 1AF1 96F6 0030 6EE9 D323 639D 1E2F FF2E) gpg --keyserver pgp.mit.edu --recv-keys 1E2FFF2E Never ask a man what OS he uses. If it's FreeBSD, he'll tell you. If it's not, why embarrass him? ..I'm sorry..
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