Re: PSA: Clock drift and pkgin

[Johnny Billquist <bqt%softjar.se@localhost>]

On 2023-12-13 15:58, Mouse wrote:
> > Well, to be honest, 106% on one process is more than an FP rounding
> > error. :D
>
> Some, at least, of the values printed by top are not measurements, but
> decaying averages of measurements.  For those, sensible sums are not to
> be expected.

Load is, yes. And that's not top specific. That's how load is defined. 
However, the time in different cpu states are actual measurements. And 
they are always looking fine, even if very heavy towards system and 
interrupt, in a way that really bothers me. We shouldn't be anywhere 
near the amount of time spent in system and interrupt that we currently 
are. It's ridicolous.

But the time and % of CPU for individual processes and not, I believe, 
plain measurements, but calculations based on other data, which can lead 
to odd values. But exactly how those numbers are done I don't remember. 
Which is why I still is hoping/expecting that someone else jumps in and 
explains them. Otherwise I'll have to go and dig around in the code to 
refresh myself...

> > > Do you have measurements that show clock drift under load?
> > I was assuming he had.
>
> When running 1.4T on my VAX emulator, I've noticed clock drift.  One of
> my "I want to do someday" things is to figure out what's going on with
> that.  (And that's 1.4T, too, not "these days".)

Do you know if that was drift affected by load, or just simple drift?
Because if you run a VAX without something like ntp, you will *always* 
have some drift. The clock interrupt on the VAX isn't very precise. It's 
running at 100 Hz, but the error is commonly a couple of percent, 
meaning over a day you can easily have a drift of a minute or two.

> One of the benefits of emulation is that I can do things like
> instrument the ICCS emulation to tell exactly how many ticks are
> missed (ie, how many ticks occur before the previous tick's interrupt
> is serviced).

That could be very interesting.

  Johnny

--
Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt%softjar.se@localhost             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol