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    SubjectRe: page fault scalability patch V8: [4/7] universally available cmpxchg on i386
    Andi Kleen wrote:
    > On Tue, Sep 21, 2004 at 06:41:25PM +0300, Denis Vlasenko wrote:
    >
    >>On Monday 20 September 2004 23:57, Andi Kleen wrote:
    >>
    >>>On Mon, Sep 20, 2004 at 01:49:20PM -0700, Christoph Lameter wrote:
    >>>
    >>>>On Mon, 20 Sep 2004, Denis Vlasenko wrote:
    >>>>
    >>>>
    >>>>>I think it shouldn't be this way.
    >>>>>
    >>>>>OTOH for !CONFIG_386 case it makes perfect sense to have it inlined.
    >>>>
    >>>>Would the following revised patch be acceptable?
    >>>
    >>>You would need an EXPORT_SYMBOL at least. But to be honest your
    >>>original patch was much simpler and nicer and cmpxchg is not called
    >>>that often that it really matters. I would just ignore Denis'
    >>>suggestion and stay with the old patch.
    >>
    >>A bit faster approach (for CONFIG_386 case) would be using
    >
    >
    > It's actually slower. Many x86 CPUs cannot predict indirect jumps
    > and those that do cannot predict them as well as a test and jump.

    Wouldn't alternative_input() choosing between a cmpxchg and a call be
    the way to go here? Or is the overhead too high in an inline function?

    (No patch included since I don't pretend to understand gcc's asm syntax
    at all.)

    --Andy
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