[Info-vax] VSI: "Official 8.4-1H1 Launch"

[Chris Scheers]

Bob Koehler wrote:
> In article <55734365$0$32453$c3e8da3$cc4fe22d at news.astraweb.com>, JF Mezei <jfmezei.spamnot at vaxination.ca> writes:
>> When working on the early boot sequence/stages, I doubt that performance
>> really matters.  And if most operating systems can run just fin on a VM,
>> it means that the VM gives it adequate CPY time slots.
>>
>> Also, remember that VMS ran on the All Mighty Microvax II, where
>> performance wasn't measure in instructions per second, but seconds per
>> instruction :-)  Pretty sure a VM can offer better performance overall
>> than an MV II.
> 
>    Yes, but a VM can intererfe with hard real-time to the extent that
>    your processor needs to be 1000 times faster.  You can probably get
>    processors 1000 times faster than an MV II now, but you can also
>    get VM interference tht's worse.

Well, yes and no.

Theoretically, in a VM, you actually run the native instruction set at 
full speed.  You only have issues if you need to enter/exit the hypervisor.

Depending on how your real-time code is written, you may be able to stay 
out of the hypervisor, especially if you have enough cores available to 
dedicate one or more to your task.

With an emulator, every instruction may be emulated and the factor of 
1000 comes a lot closer.

I do hard real-time conversions of Data General systems to an emulator, 
sometimes running under a VM, so I've seen these issues.

It seems that each real-time system is unique and quite often requires 
special tuning, but it can be done.

Interestingly, its not uncommon for the problem to be an emulation that 
runs too fast.

-- 
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Chris Scheers, Applied Synergy, Inc.

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