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    SubjectRe: [RFC PATCH 1/1] trace: Move trace event enable from fs_initcall to early_initcall
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    On Fri, Aug 17, 2012 at 10:55 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
    > On Fri, 2012-08-17 at 08:01 -0300, Ezequiel Garcia wrote:
    >
    >> Regarding the 'complete solution': to be able to capture events from
    >> the very beggining...
    >> Have you thought about this?
    >> Could you give me a hint on how could I implement it?
    >
    > How far in the "beginning"? Before memory is set up?

    Yes.

    > I wouldn't do that.

    Yeah, perhaps it sounds crazy. It makes some sense for kmem events, though.

    > I have in the past (set up before memory was finished being
    > initialized), but things have changed since then.
    >
    > One thing that we could do for those that want really early tracing, is
    > to add a config option to add a static temporary ring buffer, that gets

    Yes, something like this would be ideal. How would this ring buffer be
    allocated?
    Perhaps as static and __initdata?
    This way it would be released afterwards, right?

    > copied into the default ring buffer after memory is set up. That may be
    > the easiest way.
    >
    > Once memory is set up, the ring buffer can be allocated and events can
    > be traced, but the ring buffer needs to be set up first. All it would
    > take is some calls in init/main.c start_kernel() to the initialization.
    >

    Note that my main concern is on trace_events (kmem events to be precise).
    However this are registered through tracepoints and in turn this tracepoints
    depend on kmalloc and friends. So, right now is a chicken-egg problem.

    Thanks,
    Ezequiel.


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