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    SubjectRe: [PATCH 0/5] ftrace: to kill a daemon

    On Fri, 8 Aug 2008, Mathieu Desnoyers wrote:
    > * Steven Rostedt (rostedt@goodmis.org) wrote:
    > >
    > > I originally used jumps instead of nops, but unfortunately, they actually
    > > hurt performance more than adding nops. Ingo told me it was probably due
    > > to using up the jump predictions of the CPU.
    > >
    >
    > Hrm, are you sure you use a single 5-bytes nop instruction then, or do
    > you use a mix of various nop sizes (add_nops) on some architectures ?

    I use (for x86) what is in include/asm-x86/nops.h depending on what the
    cpuid gives us.

    >
    > You can consume the branch prediction buffers for conditional branches,
    > but I doubt static jumps have this impact ? I don't see what "jump
    > predictions" you are referring to here exactly.

    I don't know the details, but we definitely saw a drop in preformance
    between using nops and static jumps.

    -- Steve



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