FW: [Simh] SimH vax.exe cpu usage on Windows.

Wed May 19 00:54:56 EDT 2004

Hi Lewis,

I believe that you are worried about the 100% thing when you really
don't have to.

When I first touched simh, one of the first changes I submitted to
Bob was a lowering of the CPU priority on both Windows and Unix
systems when instructions are executing.  This has been in the code
base for almost 2 years now.  This is done internal to simh, so any
external efforts to lower priority are merely making it lower than it
already made itself.

Since the simh process is running at a lower priority, it will
simulate instructions only when the hosting system (Windows in your
case) is otherwise idle.  Usually the only process that "suffers"
from simh running at 100% is the system idle process, which exists
merely to soak up CPU cycles that are otherwise unused.

So, in the end, you don't really need separate system to run your VAX
continuously.

Your comments about lowering the priority having no apparent gain in
performance is true, since it is already low, you could observe the
same "no net gain" if you stopped the simh process.  Hence it really
doesn't affect anything.

Since your system is NOT a Notebook (which could benefit from
dynamically turning down clock speed when the system is idle to
reduce battery power consumption), running the CPU at 100% won't hurt
anything.  It won't create more heat, or make your disks work harder,
or anything.

Andreas suggested that if you could figure out when the simulated
system is "idle", you could get the simulator to idle itself as well.
 As I've already said this is likely not worth the effort since there
really is no net gain.

There is, however, one case where implementing such an "idle"ing
concept would benefit things.  This would come up if you somehow
wanted or needed to run more than one simulator on the same host
system simultaneously.

All of that said, I've actually have a version of simh VAX which does
support idling (or yielding) the CPU when the simulated system is
idling.  The changes to support this affect several chinks of simh
code.  I submitted it to Bob about a year and a half ago, and he
didn't see the need.

- Mark Pizzolato

--- "Bishop, Lewis" <lewis.bishop at eds.com> wrote:
> Thanks for the responses so far...
> 
> I have a dilemma whereby I cannot really justify a separate system
> as this
> is a home setup and whilst it's nice to have up and running it
> won't
> honestly get much use. The performance of the system itself is
> actually
> okay, however, at times with the load on the system it does affect
> it quite
> a bit - the system is also functioning as a PDC and exchange server
> and runs
> virtual SuSE Linux and Solaris systems with Oracle installed in
> each - so it
> does a fair bit! ;-) Memory is not a problem as it has 1gb -
> normally
> leaving 256mb (25%) free after everything else.
> 
> I'm keen to reduce the CPU as I don't like to run the CPU at 100%
> for long.
> I'm not convinced it's good for it, especially as it's not a server
> grade
> system (i.e. it's a beefed up home PC or it was when I bought it 4
> years
> ago!).  There are a number of discussions around discussing this
> type of
> usage and a lot of concerns are raised not so much over the high
> CPU usage
> but over the other system components that have to run - i.e.
> cooling fans,
> power supply etc... all of these components, having a limited
> lifetime are
> going to fail at some stage - running a fan 24/7 is obviously going
> to
> stress it more than a few hours running per day.
> 
> I have set the priority down to low and to be honest it doesn't
> seem to make
> any difference to the overall system performance. I've tried some
> of the PC
> slow utilities but these have not reduced the CPU usage (didn't
> think they
> would). If it cannot be done within SimH then maybe some form of
> resource
> manager would  be good?
> 
> Anyone have any further ideas?
> 
> Lewis Bishop
> 
> 
> -----Original Message-----
> From: Parker, David [mailto:David.Parker at stjohn.org] 
> Sent: Tuesday, 18 May 2004 4:29 p.m.
> To: Bishop, Lewis
> Subject: RE: [Simh] SimH vax.exe cpu usage on Windows.
> 
> 
> You could try setting the priority lower on the application
> process.
> Or, if performance is just that important, run it on another
> machine.
> I'm running mine (pretty much the same setup) on an old 850Mhz CPU
> and it's
> decent.
>  
> $0.02
> 
> 	-----Original Message----- 
> 	From: Bishop, Lewis [mailto:lewis.bishop at eds.com] 
> 	Sent: Mon 5/17/2004 6:20 PM 
> 	To: 'simh at trailing-edge.com' 
> 	Cc: 
> 	Subject: [Simh] SimH vax.exe cpu usage on Windows.
> 	
> 	
> 
> 	Hi all,
> 	
> 	I have OpemVMS 7.3 running under SimH v2.10-3 under Windows 2000
> with the
> 	networking option using WinPCap and a 2nd NIC. I'm really happy
> with
> the
> 	fact that i can get VMS running on a windows machine (after not
> using it for
> 	6 years or so) but i'm a bit concerned to see the cpu usage by
> vax.exe
> 	sitting at max (as much as it can get) and taking complete system
> cpu to
> 	100%.
> 	
> 	Although system performance is not 'hammered' by this (it releases
> resource
> 	when requested) the system performance has suffered slightly. I
> have
> tested
> 	the latest distribution (v3.2) but it is the same - does anyone
> know
> if
> 	there is a way to limit the CPU usage for vax.exe?
> 	
> 	Thanks,
> 	
> 	Lewis Bishop.
> 	
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> 
> 
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