Messages in this thread | | | Date | Wed, 25 Feb 2009 12:34:12 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH] new irq tracer |
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* Jason Baron (jbaron@redhat.com) wrote: > On Wed, Feb 25, 2009 at 11:48:28AM -0500, Masami Hiramatsu wrote: > > KOSAKI Motohiro wrote: > > >> /** > > >> * handle_IRQ_event - irq action chain handler > > >> * @irq: the interrupt number > > >> @@ -354,7 +358,9 @@ irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action) > > >> local_irq_enable_in_hardirq(); > > >> > > >> do { > > >> + trace_irq_entry(irq); > > >> ret = action->handler(irq, action->dev_id); > > >> + trace_irq_exit(irq, ret); > > >> if (ret == IRQ_HANDLED) > > >> status |= action->flags; > > >> retval |= ret; > > > > > > Nobdy want unnecessary redundant tracepoint. > > > Please discuss with mathieu, and merge his tracepoint. > > > > Hmm, from the viewpoint of trouble shooting, the place of LTTng's tracepoint > > is enough. However, from the same viewpoint, it should pass irq-number > > to irq-exit event too, because we may lost some previous events by buffer-overflow > > etc. > > > > trace_irq_entry(irq, NULL); > > ret = _handle_IRQ_event(irq, action); > > trace_irq_exit(irq, ret); > > ^^^^ > > > > 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.
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.
Mathieu
> thanks, > > -Jason >
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