Vmware was Re: Announcing shell machine availability for dragonfly developers

Rik van Riel riel at surriel.com
Sun Aug 31 17:26:36 PDT 2003

On Fri, 29 Aug 2003, Matthew Dillon wrote:

>     I have used bochs too.  It's been improved considerably from earlier
>     versions but, of course being an instruction-by-instruction emulator,
>     it is slower then VMWare.  On the otherhand Bochs is entirely usermode
>     and has no chance of crashing your system, something I have managed
>     to do with vmware on occassion :-).

Think of QEMU as a faster Bochs. ;)

Also, QEMU is used to run single x86 applications on
eg. PPC64 or IA64.

>     It occurs to me that we could implement a full address space abstraction
>     for DragonFly which would allow normal user programs to use the entire
>     address space.  Once that were done it would only be a small step to
>     implement a usermode 'emulation' layer which allows one user program to
>     intercept privileged instructions and address accesses that another tries
>     to run.  Then we could implement something similar to VMWare ourselves
>     and probably achieve 70-80% native operation.  It would be an interesting
>     project, anyway.

Funny you mention that.  User Mode Linux has recently
switched to this mode of operation, using separate kernel
address spaces (SKAS) for the UML "user process" and the
UML "kernel process".

Your performance estimate is right, it runs at about 75%
native speed.


"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan

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