[SeaBIOS] insn prefixes?

Kevin O'Connor kevin at koconnor.net
Sat Oct 2 16:32:08 CEST 2010

On Sat, Oct 02, 2010 at 11:39:06AM +0200, Avi Kivity wrote:
>  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?

No.  I was asking only out of curiosity.  Even if prefixes slow 16bit
mode, a normal SeaBIOS boot runs very little 16bit code.


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