[Info-vax] And another one bites the dust....

[Jan-Erik Söderholm]

Den 2022-02-16 kl. 16:58, skrev Arne Vajhøj:
> On 2/16/2022 10:44 AM, Johnny Billquist wrote:
>> On 2022-02-15 18:21, Bill Gunshannon wrote:
>>> On 2/15/22 11:00, Jan-Erik Söderholm wrote:
>>>> Den 2022-02-15 kl. 16:46, skrev Bill Gunshannon:
>>>>> On 2/15/22 10:16, Dan Cross wrote:
>>>>>> In article <j71r42Fh9vsU1 at mid.individual.net>,
>>>>>> Bill Gunshannon  <bill.gunshannon at gmail.com> wrote:
>>>>>>> Maybe, but the push seems to be for virtualization and I saw a number
>>>>>>> of OpenVMS job announcements that seemed to be production floor systems
>>>>>>> which probably can't virtualized.
>>>>>>
>>>>>> Why not?  There are reasons to virtualize systems on-prem.
>>>>>
>>>>> I guess it depends on how you actually communicate with the
>>>>> devices on the floor.  When I think of production floor systems
>>>>> I think of cables between running machines and computers.
>>>>> Probably my PDP-11 past seeping through.
>>>>
>>>> Our VMS production support system only talks over the network.
>>>> Could just as well be in a VM as on the current Alpha.
>>>>
>>>
>>> I thought of that afterwards. I guess a  lot of it today is PLC's
>>> talking to the bigger iron over the network.  But that just leaves
>>> me wondering how one does realtime.
>>
>> Throw lots of hardware resources as the problem, and pray. That's what I 
>> usually see... Usually aided by the fact that a lot of situations isn't 
>> hard realtime.
> 
> I would expect the real time characteristics to depend on the OS
> and the execution environment (read: if you want good real time
> characteristics then avoid GC) not virtualization vs non-virtualization.
> 
> Assuming a type 1 (bare metal) hypervisor and no over-commitment of
> resources (aka number CPU's in VM's <= physical CPU's present), then
> I don't see how virtualization should be a problem.
> 
> Arne
> 
> 

Right. We run "real time" against PLCs and have a round-trip time of
10-20 ms including the database processing in the Alpha VMS system.
I do not expect that to be higher in a (modern) VM x86 environment.