[Simh] several SIMH instances

[Kevin Handy]

Maurice MORETTI wrote:

>How many instances of simh can I have on one Linux machine ?
>I guess one ; isnt it ?
>  
>
You can run as many as you want, but each instance
will try to use 100% of the CPU (at least until the idle
mechanism is implemented). Thus the more instances
you add, the slower the emulation will be.

As it currently exists, simh will consume 100% of your
hosts CPU time doing its emulation. The emulated CPUs
don't stop executing instructions when idle, they
usually run an idle loop program, thus the host
CPU always sits at 100% CPU usage.

You could use a 2 processor system, which would allow
you run two copies of simh, each one consuming 100%
of one of the CPUs.

Patches are being worked on that will monitor the
emulated CPU, and when it detects it in an idle loop,
will cause the emulation to sleep. This can
greatly reduce the load on the host CPU, allowing more
instances to run without battling for CPU time, depending
on how much idle time the emulated system has.
On my system, CPU usage for simh went from 100% busy
to approx 30% busy with the idle loop code during
bootup of VMS. However this code is experimental.

>If I have a Xen architecture that will allow several Linux virtual machine;
>if each machine hae a VMS emulator, will that work ?
>  
>
Shouldn't be necessary, the problem is the 100% cpu
usage. Idle time sleep, or use of a multi-processor system
are the best ways around that problem.