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    SubjectRe: [PATCH 1/5] ftrace: Synchronize variable setting with breakpoints
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    On Thu, 2012-05-31 at 14:50 -0400, Steven Rostedt wrote:

    > > Well, the fail is before that, how could we grow two pieces of code
    > > doing similar things in the first place?
    >
    > Again, ftrace is slightly different as it does 30,000 changes at once,
    > on top of known nops. This was done through stop_machine(), thus any
    > slowdown was a large hit to system performance. text_poke() took the way
    > of mapping a page to do the change, and Mathieu didn't want to change
    > that (IIRC). But now we want the two to be similar.

    We could give text_poke a function argument to do the actual
    modification, leaving all the magic centralized.

    Also, why did Mathieu insist on keeping that kmap()?

    > > I hardly ever use dyn-ftrace but I do use some text_poke() through
    > > jump_labels.
    >
    > You don't use function tracer? That's dyn-ftrace.

    Not much no.. I do use trace_printk() and ftrace_dump_on_oops a lot
    though.

    > But still, we need to keep the record as small as possible because it is
    > persistent throughout the life of the system running. Every location
    > must be recorded, and maintain a state (flags).
    >
    > Text_poke() mostly grew out of the jump-label work. But yes, there's
    > still a lot that can be shared. The actual code modification may be.

    Afaicr we didn't change text_poke() for the jump-label stuff, except in
    trivial ways (added a #ifdef and exposed a function etc..).

    > > I would still like to end up with one code base doing CMC with two
    > > implementations depending on a Kconfig knob.
    >
    > You mean keep stop_machine around?

    Yeah, like have CONFIG_CMC_STOPMACHINE and CONFIG_CMC_FANCY for a little
    while.

    If we find a problem with the fancy approach going back is easy, once
    its proven stable we could remove the stop-machine one.


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