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    SubjectRe: [PATCH] x86: Change x86 to use generic find_next_bit

    * Alexander van Heukelum <heukelum@fastmail.fm> wrote:

    > > ok, that's rather convincing.
    > >
    > > the generic version in lib/find_next_bit.c is open-coded C which gcc
    > > can optimize pretty nicely.
    > >
    > > the hand-coded assembly versions in arch/x86/lib/bitops_32.c mostly
    > > use the special x86 'bit search forward' (BSF) instruction - which i
    > > know from the days when the scheduler relied on it has some
    > > non-trivial setup costs. So especially when there's _small_ bitmasks
    > > involved, it's more expensive.
    >
    > Hi,
    >
    > BSF is fine, it doesn't need any special setup. [...]

    under "setup costs" i mean cycles spent by the CPU itself - the
    instruction itself is simple (of course) and needs no setup. If you look
    at BSF performance you'll see that it has nontrivial overhead.

    Ingo


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