[Simh] newbie question about simh performance

[Mark Pizzolato]

On Wednesday, August 17, 2016 at 7:54 AM, gérard Calliet wrote:
> I use simh to emulate VMS software, just a compiler impossible to port out of
> VAX/VMS. The compiler uses a lot of CPU resource, and very few of the others
> resources, like IO.
> 
> I see that my jobs consume, for example, 2mn of cpu, for 2 hours of elapsed
> time, which seems bizarre because there is not a lot of IO and the compile
> task is the only one on the emulated VAX.
> 
> I run simh on itanium i4 OpenVMS, and I hoped I would have good
> performances on this fast computer.
> I see that the simh process running on OpenVMS itanium does a lot of
> (direct) IO.
> 
> Perhaps I forgot some good parameters? My .ini is minimal :
> 
> load -r ka655x.bin
> attach NVR ka655.nvr
> set cpu 512m
> set -L rq0 rauser=18000000
> attach rq0 datauser2.dsk
> set xq mac=08-00-2B-3C-96-78
> attach xq eth1
> b cpu
> 
> 
> Any help will be welcomed, advice, documentation...

HI Gérard,

First, you don't specify which simh version you're using.
The output of:

              sim> SHOW VERSION

would be useful.

Second, although you've configured the simulated VAX to 
have 512MB of RAM, you may or may not have the VMS 
OS that you're running 'tuned' to leverage that RAM.

Third, the way you're using the system to 'compile' things
may not be leveraging the potential to consume CPU cycles.
The simh 4.x codebase is capable of asynchronous disk I/O
which can allow other activities on the simulated system 
to use the CPU while one process is waiting for I/O.  If your
compile activities aren't running multiple compiles in 
parallel then the CPU will sit idle while it waits for I/O to 
complete.

- Mark