Danny, I have a dual processor Intel here running FreeBSD that works really sweet. Intel now recommends tying the clock reading and update function to one processor and presumably that's what FreeBSD did. I disagree with that; my design for the multiprocessor Alpha, now in HP Tru64, didn't need to do that. Details in the nanokernel distribution at www.eecis.udel.edu/~mills/resource.html. Presumably, this is where the precision kernel code first originated, as the code I see in the various kernels bears an uncanny resemblance.
Dave Danny Mayer wrote: >Janusz U. wrote: > > >>Hello. >> >>I am trying to understand changes between NTP 4.1.1 and 4.1.1/4.2.0 >>versions. >>When we use FreeBSD6 and NTP 4.1.1 (eg. NIST) we will get higher >> >> > >Where does NIST come in here? > > > >>precision which here is calculated from TSC frequency. But for new NTP >>the precision will be lower (calculated from "call/jumps" time). I can >>see some redefinition of the default precision meaning. >> >> >> > >I suspect that this may be due to the fact that on a multiprocessor the >TSC which is on each processor are unsynchronized with each other and >therefore you will get different results when you call gettimeofday() >depending on which processor you are one when making the request. There >are various methods that can be use to resynchronize them or require >that only one be used when setting or reading the clock. I suspect that >attempts where made to address this but I cannot be sure since I was not >involved at the time. Dave Mills would know for sure. > > > >>NTP - Network time protocol Changeset details for 1.706.1.10 >>http://ntp.bkbits.net:8080/ntp-dev/?PAGE=gnupatch&REV=1.706.1.10 >> >>--- 1.99.1.1/ntpd/ntp_proto.c 2001-09-20 13:09:36 -07:00 >>+++ 1.99.1.2/ntpd/ntp_proto.c 2001-10-08 19:36:19 -07:00 >> >>http://ntp.bkbits.net:8080/ntp-dev/ntpd/ntp_proto.c?PAGE=diffs&REV=3bc262a3RdhnVfTzQgIi8IXLNzMIIA >> >>Was it caused by SMP vs TSC appearing? Why was FreeBSD focused only? >>Random/noise for get_systime() / clock_gettime() appeared 4-5 years >>later so it seems not related to the default precision exactly. >> >> >> > >Most likely issues related to multiprocessors but this code is 8 years >old so it is hard to know. > >Danny > > > _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions