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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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