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    SubjectRe: [PATCH] Only process_die notifier in ia64_do_page_fault if KPROBES is configured.
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    On Saturday 27 August 2005 01:05, Christoph Lameter wrote:
    > On Fri, 26 Aug 2005, Rusty Lynch wrote:
    > > Just to be sure everyone understands the overhead involved, kprobes only
    > > registers a single notifier. If kprobes is disabled (CONFIG_KPROBES is
    > > off) then the overhead on a page fault is the overhead to execute an
    > > empty notifier chain.
    >
    > Its the overhead of using registers to pass parameters, performing a
    > function call that does nothing etc. A waste of computing resources. All
    > of that unconditionally in a performance critical execution path that
    > is executed a gazillion times for an optional feature that I frankly
    > find not useful at all and that is disabled by default.

    In the old days notifier_call_chain used to be inline. Then someone looking
    at code size out of lined it. Perhaps it should be inlined again or notifier.h
    could supply a special faster inline version for time critical code.

    Then it would be simple if (global_var != NULL) { ... } in the fast path.
    In addition the call chain could be declared __read_mostly.

    I suspect with these changes Christoph's concerns would go away, right?

    -Andi
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