[Simh] CPU throttle and idle on VAX

Jason Stevens neozeed at gmail.com
Thu Dec 4 10:42:37 EST 2008


There was a long rolling thread a back around september 24th about VMS 4.7
and the idle, where I'd mentioned a smallish fix.. It does require
rebuilding the source though.

The fix had worked for me running BSD 4.3 RENO, and I'm assuming Gerry is
running ok now on VMS 4.7 as I haven't heard anything.

Basically you need to regress the settings in vax_cpu.c ...

in version 3.7-1 (and friends) you'll find it was
uint32 cpu_idle_ipl_mask = 0x8;                         /* idle if on IPL 3
*/
int32 cpu_idle_wait = 1000;                             /* for these cycles
*/

to in 3.8
uint32 cpu_idle_ipl_mask = 0xB;                         /* idle if on IPL 3
*/
int32 cpu_idle_wait = 200;                             /* for these cycles
*/

So go ahead and change the 0xB to 0x8 & the 200 to 1000.
Lastly you need to alter the following table in vax_cpu.c from this:

static struct os_idle os_tab[] = {
    { "VMS", 0x8 },
    { "NETBSD", 0x2 },
    { "ULTRIX", 0x2 },
    { "OPENBSD", 0x1 },
    { "32V", 0x1 },
    { NULL, 0 }
    };

to this:

static struct os_idle os_tab[] = {
    { "VMS", 0xB },
    { "NETBSD", 0x2 },
    { "ULTRIX", 0x2 },
    { "OPENBSD", 0x1 },
    { "32V", 0x1 },
    { NULL, 0 }
    };

Then just run it set as 'VMS' and it'll be SIMILAR to how it was in the
older versions.  I'm 99% sure of that is what I did, but currently the
machine I'm on doesn't have usleep so I cannot verify 100%... I'll check
later.

Jason





On Thu, Dec 4, 2008 at 4:19 AM, roy hills <royhills at hotmail.com> wrote:

> 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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