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    SubjectRe: [PATCH 4/6] hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events
    On Thu, Nov 05, 2009 at 10:59:44AM +1100, Paul Mackerras wrote:
    > Frederic Weisbecker writes:
    >
    > > This patch rebase the implementation of the breakpoints API on top of
    > > perf events instances.
    > >
    > > Each breakpoints are now perf events that handle the
    > > register scheduling, thread/cpu attachment, etc..
    >
    > What I haven't managed to understand yet is how you provide reliable
    > breakpoints for debugging purposes. If I'm debugging a program and I
    > have set a breakpoint, I'll be very unhappy if the breakpoint should
    > trigger but doesn't because the perf_event infrastructure has decided
    > it can't schedule that breakpoint in. If the breakpoint isn't going
    > to work then I want to know that at the time that I set it.
    >

    The hw-breakpoint layer avoids such issues by not over-committing debug
    registers i.e. 'n' number of debug registers are reserved for user-space
    where n = max(no. of breakpoints requested by any given process/thread).
    And book-keeping certainly helps here too.

    Thanks,
    K.Prasad



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