[Info-vax] OS implementation languages

[Bob Gezelter]

On Wednesday, August 30, 2023 at 4:58:45 PM UTC-4, Arne Vajhøj wrote:
> On 8/30/2023 4:53 AM, Johnny Billquist wrote: 
> > Not sure how easy it is to dodge RMS under VMS. In RSX, you can just do 
> > the QIOs to the ACP yourself and go around the whole thing, which makes 
> > I/O way faster. Of course, since files still have this structure thing, 
> > most of the time you are still going to have to pay for it somewhere. 
> > But if you are happy with just raw disk blocks, the basic I/O do not 
> > have near as much penalty. Admitted, the ODS-1 (as well as ODS-2) 
> > structure have some inherent limitations that carry some cost as well. 
> > So you could improve things some by doing some other implementation on 
> > the file system level. 
> > But mainly, no matter what the file system design is, you are still 
> > going to have the pain of RMS, which is the majority of the cost. And 
> > you'll never get away from this as long as you use VMS.
> SYS$QIO(W) for files works fine on VMS too. 
> 
> But a bit of a hassle to use. 
> 
> There are two alternative ways to to bypass RMS: 
> * SYS$IO_PERFORM(W) - the "fast I/O" thingy 
> * SYS$CRMPSC - mapping the file to memory 
> 
> Arne
Arne,

One can bypass RMS, but it is not RMS that is the inherent problem. In my experience, it is not so much using RMS, but using RMS poorly that is the source of most problems.

As I noted in another post in this thread, increasing buffer factors and block sizes often virtually eliminates "RMS" performance problems. File extensions are costly, extending files by large increments also reduces overhead, increasing performance.

Not solely an OpenVMS problem. Originally dealt with this problem on IBM's OS/360 when I was a high school student. Reduced the cost of a production job by multiple orders of magnitude by simply increasing a blocking factor from 1 to 100. Yield? Two orders of magnitude reduction in CPU time consumed.

The other day I needed to copy a bare partition on a linux system. When refreshing my recollection of dd, noted that dd, for historical reasons, copies one block at a time. Increased performance by reading/writing a megabyte at a time. 

It is often not the depth of the stack that matters, but how often one traverses the stack from top to bottom.

- Bob Gezelter, http://www.rlgsc.com