Messages in this thread | | | Date | Thu, 26 Feb 2009 17:20:47 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH] new irq tracer |
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On Thu, Feb 26, 2009 at 10:11:05AM -0500, Jason Baron wrote: > On Wed, Feb 25, 2009 at 12:34:12PM -0500, Mathieu Desnoyers wrote: > > * 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. > > > > maybe...although that would require re-arranging the 'while' loop in > 'handle_IRQ_event' from a do..while loop to a 'while' loop, which will > require an extra branch check, and then we still have to record the last 'ret' > value. I'm not that keen on re-arranging this for trace data... > > Using Steve's new 'DEFINE_TRACE_FMT', I can get function graph trace > as follows using the original two tracepoints (patch below): > > 3) | handle_IRQ_event() { > 3) | /* (irq_handler_entry) irq=28 handler=eth0 */ > 3) | e1000_intr_msi() { > 3) 2.460 us | __napi_schedule(); > 3) 9.416 us | } > 3) | /* (irq_handler_exit) irq=28 handler=eth0 return=handled */ > 3) + 22.935 us | } > > thanks, > > -Jason >
I'm impressed by this new TRACE_FMT system. It means that I will just need to toggle a value on a /debug/trace/events/irq_stuff/enable to have the useful informations as comments inside a trace, or in a whole dedicated traces.
I've played with it a part of the night to test the bprintk patch, this is awesome!
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