[Info-vax] CRTL and RMS vs SSIO

[Stephen Hoffman]

On 2021-10-11 17:29:52 +0000, Simon Clubley said:

> On 2021-10-08, Lawrence D?Oliveiro <lawrencedo99 at gmail.com> wrote:
>> On Saturday, October 9, 2021 at 4:37:26 AM UTC+13, Stephen Hoffman wrote:
>>> Having looked at this back in the VAX era, the slow process creations 
>>> our apps were incurring were arising from inefficiencies within the DCL 
>>> spawn-related processing, and not from within the OpenVMS process 
>>> creation overhead.
>>> 
>>> Once that was identified and the obvious work-around implemented, 
>>> spawns were pretty speedy even VAX-era.
>>> 
>>> To Simon's comment, how DCL gets mapped into process address space is 
>>> just ugly, too. And hard to debug.
>> 
>> But the whole reason why DCL maps into a process in this way, so that 
>> user-mode code can be repeatedly loaded, run and then wiped from the 
>> same process, was precisely to avoid multiple process creations.

Supervisor-mode interpreters and user-mode memory management rundown 
does allow user context to be maintained across a series of 
executables, yes.

There are obviously other ways for an operating system to maintain user 
context across a series of executable image invocations, of course.

>> Now you are saying that the DCL mechanism itself contributes to the 
>> overhead of process creations!

The subprocess creation performance issue that was effecting the local 
VAX systems was found due to an internal design choice within DCL 
itself.

Not an architectural-level choice.

That design choice could conceivably be altered, should spawn 
performance be a performance-limiting factor for a sufficiently-large 
customer.

Modern hardware is a whole lot faster than any VAX ever was, so—outside 
designs that create and then run down massive numbers of processes—the 
whole "process creation" discussion has largely faded.

> Sort-of wiped. Turns out that's a rather important difference. :-)
> 
> BTW, spawn is when you actually do want a new subprocess for some 
> reason. Not the same thing as loading an image into the existing DCL 
> process.

Folks around here do seem to be learning both about OpenVMS and about 
Linux in recent threads, too. 😈


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