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    SubjectRe: [PATCH] new irq tracer
    > > the lttng tracepoints wrap the calls to _handle_IRQ_event in 3
    > > different places. So the above suggested irq tracepoint provides the
    > > same information with 4 less tracepoints in the code. So I believe its
    > > simpler - plus we can understand which action handlers are handling the
    > > interrupt.
    > >
    > The main thing I dislike about only tracing action->handler() calls is
    > that you are not tracing an IRQ per se, but rather the invocation of a
    > given handler within the interrupt. For instance, it would be difficult
    > to calculate the maximum interrupt latency for a given interrupt line,
    > because you don't have the "real" irq entry/exit events, just the
    > individual handler() calls.

    I agree with IRQ latency tracing is very important.
    So now, We understand we have another two good requirement.

    Therefore, I can agree to Mathieu's separete trace point idea and
    Jason's current patch.

    Thanks! good discussion.

    > But I agree that knowing which handler is called is important.
    > How about this compromise :
    > trace_irq_entry(irq, action)
    > _handle_IRQ_event()
    > for each action {
    > trace_irq_handler(action, ret);
    > ret = action->handler(irq, action->dev_id);
    > ...
    > }
    > trace_irq_exit(action_ret);
    > Would that give you the information you need ?
    > Here trace_irq_handler would be passed the _current_ action invoked and
    > the _previous_ action return value. Note that we should initialize
    > irqreturn_t ret to some initial value if we do this. That should keep
    > the tracing overhead minimal.

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