lkml.org 
[lkml]   [2009]   [Feb]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] new irq tracer
* 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
>

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


\
 
 \ /
  Last update: 2009-02-25 18:37    [from the cache]
©2003-2011 Jasper Spaans