[SeaBIOS] insn prefixes?
avi at redhat.com
Sat Oct 2 11:39:06 CEST 2010
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.
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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