Messages in this thread | | | Date | Wed, 25 Feb 2009 17:12:10 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH] new irq tracer |
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* Steven Rostedt (rostedt@goodmis.org) wrote: > > > On Wed, 25 Feb 2009, 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. > > Then use the function_graph tracer. >
Sadly, the function tracer cannot be enabled on production systems. Therefore it's not a usable solution in the context where I need this.
Mathieu
> # echo smp_apic_timer_interrupt > /debug/tracing/set_ftrace_filter > # echo __irqentry_text_start >> /debug/tracing/set_ftrace_filter > # echo function_graph > /debug/tracing/current_tracer > # cat /debug/tracing/trace > > # tracer: function_graph > # > # CPU DURATION FUNCTION CALLS > # | | | | | | | > ------------------------------------------ > 1) kblockd-4012 => <idle>-0 > ------------------------------------------ > > 1) ==========> | > 1) + 35.783 us | smp_apic_timer_interrupt(); > ------------------------------------------ > 2) kstop/2-4013 => <idle>-0 > ------------------------------------------ > > 2) ==========> | > 2) + 13.819 us | smp_apic_timer_interrupt(); > ------------------------------------------ > 3) kstop/3-4014 => <idle>-0 > ------------------------------------------ > > 3) ==========> | > 3) + 24.919 us | __irqentry_text_start(); > ------------------------------------------ > 0) kstop/0-4011 => <idle>-0 > ------------------------------------------ > > 0) ==========> | > 0) + 24.444 us | smp_apic_timer_interrupt(); > ------------------------------------------ > 1) <idle>-0 => bash-3899 > ------------------------------------------ > > 1) ==========> | > 1) + 13.642 us | smp_apic_timer_interrupt(); > 2) ==========> | > 2) + 15.014 us | smp_apic_timer_interrupt(); > 3) ==========> | > 3) + 31.004 us | smp_apic_timer_interrupt(); > ------------------------------------------ > 0) <idle>-0 => sshd-3892 > ------------------------------------------ > > 0) ==========> | > 0) + 15.655 us | __irqentry_text_start(); > 0) ==========> | > 0) + 37.722 us | __irqentry_text_start(); > ------------------------------------------ > 0) sshd-3892 => <idle>-0 > ------------------------------------------ > > 0) ==========> | > 0) + 26.139 us | __irqentry_text_start(); > 3) ==========> | > 3) + 27.240 us | __irqentry_text_start(); > 3) ==========> | > 3) + 21.987 us | __irqentry_text_start(); > > > And there you have your latencies ;-) > > With Jasons added trace points, we could add the to the event tracer > and those would show up as comments here. > > -- Steve > > > > > > > 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 Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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