Re: PSA: Clock drift and pkgin

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> Some, at least, of the values printed by top are not measurements,
>> but decaying averages of measurements.
> Load is, yes.  And that's not top specific.

Agreed.

> However, the time in different cpu states are actual measurements.

The ones in the CPU states bar, yes.  But JMoyer@, as quoted by
paulkoning@, said "The values in the CPU and WCPU columns don't sum up
to the percentages in the CPU states line at the top of the display".
In my experience the WCPU and CPU columns also act like decaying
averages, though I don't know details decay algorithm, in which case
that failure to add up is no surprise at all even if timekeeping is
perfect.

Test case: Run an infinite loop.  Suspend it - don't kill it, or it
will disappear entirely - and notice that the WCPU and CPU values,
which if pure measurements should be zero the second replot after you
suspend it (the first replot will have a partial interval of busy and a
partial interval of stopped), take some time to decay.

At least they do for me, on 9.1, 5.2, and even 1.4T.  I'm pretty sure
they have on every variant of top I've tried using.

>>>> 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.
>> [...]
> Do you know if that was drift affected by load, or just simple drift?

I had the impression it was affected by load, but I didn't investigate
in enough detail to be sure.

> Because if you run a VAX without something like ntp, you will
> *always* have some drift.

If you run pretty much _any_ computer without something to keep it
synced, you will.  It's just a question of whether the hardware is
precise enough for the drift to be obvious.

>> One of the benefits of emulation is that I can do things like
>> instrument the ICCS emulation [...]
> That could be very interesting.

I'll have to do that.  When I can pry some round tuits free, of course.

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