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Re: [Qemu-devel] About qemu emulation speed (a question) and supported O

From: Jim C. Brown
Subject: Re: [Qemu-devel] About qemu emulation speed (a question) and supported OS
Date: Wed, 14 Sep 2005 18:42:03 -0400
User-agent: Mutt/1.4i

On Wed, Sep 14, 2005 at 01:46:58PM -0500, Anthony Liguori wrote:
> You can't readahead beyond a basic block.  Taking a trap for each basic 
> block and translating the block is what QEMU does.

No, QEMU translates everything from guest machine code into its internal codes.

I'm talking about using read ahead to change only those instructions which cause
problems, and replacing them with instructions that are from the same 

I suppose you could call that emulation in a sense (as ur emulating the 
instructions with other ones that create the behavior you need) but it is not
the same as what QEMU currently does.

Of course, VMware also emulates hardware, but you'd have to do that no matter
what technique you use and it is a separate issue from emulation vs translation
vs virtualization. (Theoretically VMware could just use a HAL layer like Xen
does (or the newer plex86 did) and still be a virtualizer, but then it wouldn't
work with unmodified guest OSes.)

> Regards,
> Anthony Liguori

Infinite complexity begets infinite beauty.
Infinite precision begets infinite perfection.

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