Re: [SeaBIOS] insn prefixes?

[Avi Kivity]

On 09/30/2010 05:51 AM, Kevin O'Connor wrote:
> On Wed, Sep 29, 2010 at 08:19:33AM -0700, H. Peter Anvin wrote:
> > Yeah... big real mode is rather expensive in terms of the 66 and 67
> >  prefixes you end up littering the code with just to be in the mode you
> >  actually want.  Better then to load a GDT, flip CR0.PE, and go to a
> >  32-bit code segment anyway.
>
> That brings up an interesting question.  Do you know if instruction
> prefixes result in slower cpu execution?

Is there really a performance problem in seabios?

On modern processors the only problems are with "length-changing 
prefixes", a prefix that changes the instruction length.  Usually when 
an immediate changes from 16 bits to 32 bits or vice versa.