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.