[Simh] CPU throttle and idle on VAX

[roy hills]

I'm running 4.3BSD (Quasijarus) on SIMH VAX.  I also run 2.11BSD on SIMH PDP11.  I'm using the latest version of SIMH, v3.8.

On the 2.11BSD/PDP system I use "set throttle 4M", which gives a very responsive system (probably faster than a real PDP11) while using minimal host CPU.

I find I cannot use "set throttle" on the VAX: SIMH accepts the command, but it doesn't do anything.  I need to use "set cpu idle" instead, but this is OS-specific, and I cannot find a good setting for 4.3BSD.  The best seems to be 32V, which gives me 70% host CPU usage when the OS is idle.

I have two questions:

1. Is there any reason why "set throttle" cannot be implemented for VAX?  I notice that the SIMH documentation says "Throttling and idling are mutually exclusive" - does this mean that a given simulator can only implement one method, or that only one may be used at a time?

2.  Does anyone know the best idle option for 4.3BSD?  Is there any documentation on what the various idle types detect, so an unsupported OS can be examined to see which it matches best?




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