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    SubjectRe: Linux Kernel Microcode Question
    On Mon, 22 Mar 2004, Timothy Miller wrote:
    > I don't see anything wrong with what he said. As I understand it,
    > Pentium 4 CPUs don't use microcode for much of anything. If an
    > instruction which was done entirely in dedicated hardware was buggy, and
    > it's replaced by microcode, then it will most certainly be slower.
    >
    > You seem to have missed where David used terms like "theoretically
    > possible" and "an operation".

    No, that is not what he said and that (what you say) is certainly wrong,
    namely this bit:

    If an instruction which was done entirely in dedicated hardware was
    buggy, and it's replaced by microcode, then it will most certainly be
    slower.

    All instructions are done by means of microcode of some sort, i.e. the
    instructions are "compiled" as they are executed into a more primitive
    instruction set (called "microcode" or "u-code"). If a buggy instruction
    (or rather the sequence of microcode which corresponds to it) is replaced
    by a fixed version (i.e. by some other sequence of microcode) then there
    is no reason to say that the result will "most certainly be slower". For
    some bugs the fix runs faster than the broken code, for others it may be
    slower --- there is no way to tell apriori that it will always be slower.

    Do you understand now?

    Kind regards
    Tigran
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