[Info-vax] clock problems with OpenVMS x86 on VirtualBox

[Johnny Billquist]

On 2023-05-12 22:25, Clair Grant wrote:
> On Friday, May 12, 2023 at 1:30:37 PM UTC-4, Simon Clubley wrote:
>> On 2023-05-12, Dave Froble <da... at tsoft-inc.com> wrote:
>>> On 5/12/2023 8:14 AM, Simon Clubley wrote:
>>>> On 2023-05-12, Jan-Erik Söderholm <jan-erik.... at telia.com> wrote:
>>>>>
>>>>> Actually, that was how I thought it worked. Since I observed that
>>>>> the clock in my VirtualBox VMS environment lagge a bit behind
>>>>> but each 10-20 sec, it jumpt ahead and skipped a second so that
>>>>> it become in sync with the host Windows environment again.
>>>>>
>>>>
>>>> That's going to make for some "interesting" real-time program behaviour... :-)
>>>>
>>>> Simon.
>>>>
>>>
>>> Do you think any serious real time programmer will run a real time task inside a
>>> VM? I'm not a real time programmer, and I'd still not do that.
>>>
>> As well as traditional real-time stuff (which I agree with you about BTW),
>> there's also communications with external devices and the timestamping of
>> received messages, both of which could be affected by such jumps.
>> Simon.
>>
>> -- 
>> Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
>> Walking destinations on a map are further away than they appear.
> Virtual Box 7.0.6, Lenovo ThinkBook, Windows 11
> 
> I put SHOW TIME in a 10 minute loop and ran it 7 hours. Every output showed exactly 10 minutes and 0 seconds from the previous. I did the same thing on
> 
> ESXi 8.0, DL580
> 
> and got the same result. If we have a problem, it is certainly not universal.

You can hide a lot of potential problems with really fast hardware. 
Don't mean the problems don't exist.

You want me to demonstrate this to you? Give me access to your host 
system where these VMs are running, and I'll throw some monkey wrenches 
in your timing... ;-)

Also, over time, the VMs compensate for jitter and drift, so over time, 
you should be still be good for the type of test/measurement you did.

   Johnny