[Simh] SimH and multi-core host processors

[Gary Lee Phillips]

I just looked through the introductory documents and found no mention
of running SimH emulations on hosts with multi-core processors. Is
SimH aware of the fact that it is running on such a CPU?

I downloaded the OpenBSD for vax CD image yesterday. Having a
Raspberry Pi 2 Model B sitting here and not getting much use, I
decided (probably foolishly) to use it to install OpenBSD to a vax
disk image file. I have SimH 3.8.1 on the Pi, which has an ARM V7 quad
core processor and 1GB of RAM. I had copied my VAX configuration file
over from a single core Linux machine, and modified that to set up for
the OpenBSD install.

Normally on a single core 32-bit machine I use "set throttle 60%" to
avoid overloading the system if the SimH emulated machine becomes
compute bound or starts idle looping.

I was surprised at how slow the OpenBSD installation routine ran. In
fact, once I got it going, it has been running for over 24 hours now
and is still unpacking required system files from the compressed tar
(.tgz) archive files on the CD. Progress is made, but slowly. Tonight
it dawned on me to check the CPU utlization meter on the Linux host.
Sure enough, with only the installation running on SimH, the CPU was
limited at 15% utlization and would not go above that level. If one
core is 25% of the whole CPU capability, and I use only a maximum of
60% of one core, that comes out to 15%, the point at which the system
throttles back whether it is busy or not. So, I'm guessing, if I
remove the "set throttle" statement from the configuration, the
maximum CPU capability SimH will use for a single instance is still
limited to 25% of the machine's total capability. Does that make
sense?

I will test this myself, but can't do so until I finish with
installing OpenBSD.

Is there any way to get a single instance of SimH to run across
multiple cores? Or is it just single threaded so it is limited to
running on a single core at any time?
--Gary