[ntp:questions] Re: clock resolutions for different OS

Steve Woodford steve at mctavish.co.uk
Wed Aug 20 08:56:10 UTC 2003


ptrojane at mion.elka.pw.edu.pl (Piotr Trojanek) writes:

>In article <bhu3m2$vao$1 at cesium.transmeta.com>, H. Peter Anvin wrote:
>>Most CPUs these days have a counter which counts individual core clock
>>cycles.

>True, but there still is a question, does OS support this hardware...
>In example, NetBSD has microtime() routine in kernel. On i386
>architecture (which includes modern CPU with TSC instruction) it
>doesn't use core clock counter, and this routine is used both by NTP
>syscalls and PPS timestamping.

Partially correct. On x86 CPUs, NetBSD-1.6.x, and earlier releases, use
the traditional timer-based microtime(). NetBSD-current on x86 uses the
cpu cycle counter, if available (and known to be trustworthy).

Cheers, Steve



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