[Simh] Alpha simulator performance

[Sergey Oboguev]

> While we're in "wish list" mode, I'd like to see SimH emulate Alpha or Itanium, 
>
>so I could use it to run  newer versions of OpenVMS than 7.3. There are free 
>versions of commercial Alpha emulators available, but they only run on Windows 
>(BLEAH) and their performance is intentionally limited, presumably to get people 
>
>to buy the full version.

If you are concerned about performance, it is unlikely that SIMH implementation 
of Alpha (which apparently is in works, but hard to guess when it might become 
available) will "ever" match the performance of free versions of commercial 
emulators. The latter do JIT binary compilation, whereas SIMH performs 
interpretation of instruction stream and is unlikely to have JIT for the 
foreseeable 

future if ever at all.

FreeAXP performance may be throttled down compared to full Avanti, but it is 
still very fast -- much, much faster than SIMH VAX alongside it.

Also note that FreeAXP is about 3x faster when running on 64-bit version of 
Windows compared to being executed on 32-bit Windows (just as can be expected 
for the emulation of 64-bit processor).

To give a rough idea, here were the results CHARON/SRI benchmark executed on
FreeAXP running on i7 2600, 3.40 GHz on 64-bit Windows:

    Test started [...] for a AlphaServer 400 4/166 CPU with VMS V8.3

    Sequential test results:

              Whetstones   Dhrystones   VUPs
    Run 0          81.7        203735      144.5
    Run 1          80.3        200222      144.5
    Run 2          79.0        203735      144.0
    Run 3          80.3        200222      145.0
    ---------------------------------------------
    Average        80.3       201978      144.5

    Interleaved test results:

              Whetstones   Dhrystones   VUPs
    Run 0          81.7        200222      145.0
    Run 1          80.3        203735      145.0
    Run 2          80.3        203735      144.5
    Run 3          81.7        200222      144.5
    ---------------------------------------------
    Average        81.0       201978      144.8

By the way of comparison, same test executed in native Windows x64 mode on the 
same machine (with SSE code generation disabled during compilation) produced 
only 150 000 Dhrystones ;-), albeit was 150 times faster than virtual Alpha on 
Whetstones.

As a side note, I personally was never quite able to understand the reasoning of 

people who extoll VMS and simultaneously "bleah" about "Windoze", which after 
all at its foundations is to a significant extent a clean and neat 
reimplementation of 

VMS/Mica architecture at a new technological volution.