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    SubjectRe: [ltt-dev] Re: [PATCH] LTT for 2.5.38 1/9: Core infrastructure
    Linus Torvalds writes:
    > >From what I've seen from the LTT thing, it's too heavy-weight to be good

    Not true anymore.

    > I suspect we'll want to have some form of event tracing eventually, but
    > I'm personally pretty convinced that it needs to be a per-CPU thing, and
    > the core mechanism would need to be very lightweight. It's easier to build
    > up complexity on top of a lightweight interface than it is to make a
    > lightweight interface out of a heavy one.

    We have removed locks (code now atomically reserves space in the trace
    buffer), significantly reduced the cost of taking timestamps by using the
    real-time clock, and are in the process of implementing per-CPU buffers.
    As per previous email, the intent is to get only the core infrastructure
    into the kernel and keep trace points as patches. Some of the work going
    into LTT is modeled after the tracing infrastructure in K42, which is
    extremely lightweight, lock-free, and designed for multiprocessors.

    Robert Wisniewski
    The K42 MP OS Project
    Advanced Operating Systems
    Scalable Parallel Systems
    IBM T.J. Watson Research Center
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