VM and performance (was Re: [Beowulf] best Linux distribution)

Jim Lux James.P.Lux at jpl.nasa.gov
Tue Oct 9 13:31:48 PDT 2007

At 08:46 AM 10/9/2007, Bogdan Costescu wrote:
>On Tue, 9 Oct 2007, Jeffrey B. Layton wrote:
>>The last word I heard is that performance takes a substantial hit 
>>if you are running a code in a VM.
>I attended a talk some years ago by the Bochs author and I remember 
>him saying that one possibility of speeding up the virtual code is 
>to cache the code after "processing" it the first time - this could 
>work very well for a computational code if the performance sensitive 
>inner loop is treated this way. This was especially important for 
>cases where the virtual and native hardware were not the same architecture.

I believe that this isn't particularly new.  Back when folks were 
writing 1401 emulators to run on S/360 for instance, or PDP-11 
emulators creating a virtual RSX-11/RT-11 environment on PCs that was 
a fairly standard strategy.

Especially if the code is generated by a compiler and code is easily 
separable from data, it's sort of like building a specialized 
compiler from PDP-11 object to x86 object and then adding in a WINE- 
or Cygwin- like OS services layer.  Self modifying code is, of 
course, somewhat of a challenge...<grin>

James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875 

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