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    SubjectRe: {PATCH] Re: wasting time on page fault
    Linus Torvalds wrote:
    > > The assembler doesn't use nops for alignment -- it inserts longer
    > > instructions that are effectively nops, either 1 or two. For larger
    > > stretches, the assembler inserts a jmp itself for alignment.
    > Note that some of them are not very good no-ops. At least at some point
    > the "long" no-op was
    > lea 0x00000000(%esi),%esi
    > and you could cause AGI stalls and non-pairing with two of them in a row -
    > making the long no-op sequence potentially quite slow.

    When it must emit two no-ops in a row, it uses %esi and then %edi so
    there's no AGI from that. However, the assembler doesn't check
    preceding instructions to pick a decent register for the no-op
    instruction. Solution: avoid writing to %esi before an alignment op.

    > It may be that the special "lea" no-op is also recognized as such in newer
    > CPU's, but it wasn't in the early ones.

    Does Crusoe recognise that? :-)

    -- Jamie
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