[ntp:questions] Flash 400 on all peers; can't get ntpd to be happy
ralph at depth.net
Mon Mar 14 00:37:42 UTC 2011
Maybe what I'm misunderstanding is the 'how' of that measurement? And I correct
that the assumption in all this is that the system clock ticks are consistent?
And that is the root of the problem in getting things to work properly on a VM?
In reading the NTP spec it sounded to me like the formula involved taking the transmission from the client (org), receipt at server (rec), server transmit (xmt), and client receipt (dst). The problem lying with the fact that if the
clock ticks on the client aren't consistent, then the client realistically
doesn't know that the distance between org and rec is even comparable to the
distance between xmt and dst, correct? And further the client can't tell during
which segment of time the variation in time occurred, right?
I've been doing a little playing around with hwclock and adjtimex to see what the
various clocks are really doing. What it looks like is that the hardware clock
is reporting time accurately (over time at least) even though the system clock
isn't. I'm assuming that this is because under the covers the VM is having the
hardware clock report time in sync with the clocking on the host.
So maybe if we could have a mode where ntpd uses the hardware clock to measure the round trip and instead of the system clock? Or just uses the hardare clock
as the reference? And then adjusts the system clock to be closer to accurate?
In this way if you have a host system that is properly adjusted so that the
hardware clock of the VM is reporting fairly accurrately, then you ought to be
able to get ntpd to adjust the system clock to properly reflect the time.
I know this is similar to what one can do with adjtimex, but it would be nice
if there was a way to have this done properly without having to work adjtimex
manually and determine 'by hand' what the right values are.
So now I'm probably going to get told to go find the adjtimex newsgroup... but since this is time related, I hope that maybe you will continue to humor me.
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