[Info-vax] Volatile, was: Re: yet another sys$qiow question

[David Froble]

Bob Gezelter wrote:
> On Friday, August 28, 2015 at 5:02:43 PM UTC-4, Bob Gezelter wrote:
>> On Friday, August 28, 2015 at 4:36:34 PM UTC-4, Bob Koehler wrote:
>>> In article <55e0994f$0$17002$b1db1813$2411a48f at news.astraweb.com>, JF Mezei <jfmezei.spamnot at vaxination.ca> writes:
>>>> And when discussing with people who deal in real time, they are all
>>>> adament that it must all be an event loop, no ASTs allowed. So while I
>>>> never had to do this, I think it is possible that some types of apps
>>>> might actually do need to poll the IOSB as part of their real time event
>>>> loop. (if it is more efficient than checking event flags).
>>>    Did tons of ASTs in real-time.  Hard real-time.  I'd never want an
>>>    event loop.
>>>
>>>    But I know a few who don't understand there systems and do want an
>>>    event loop.
>> Bob,
>>
>> Most of the "event loop" type code originally comes from other systems without ASTs or similar constructs. X-Windows originates in a time when there was no standard Unix threading package.
>>
>> For the record, I have yet to see a case (in over 40 years of systems programming on RSX-11/OpenVMS) where AST delivery overhead was a significant factor. There have been cases where poor planning led to long latencies in AST state (e.g., WAIT-style directives, long computations), but those were poor designs, not a problem with AST efficiency.
>>
>> - Bob Gezelter, http://www.rlgsc.com
> 
> Clarification.
> 
> I DID get a call from Operations once. It seems that the AST implementation was TOO efficient (on a MV II).
> 
> It seems that an AST-based process I had implemented had been observed to not accumulate ANY CPU time over a multi-hour period. The operations team was convinced the code was hung (in actuality, it was processing tens of ASTs/second). Operations calmed down when I pointed out that the DIO count was increasing on a consistent basis.
> 
> - Bob Gezelter, http://www.rlgsc.com

If I understand it correctly, and remember things a bit, on VAX it's a hardware 
trap, correct?  What could be faster?