linux-kernel - Re: [Patch 2/2] tracepoints for softirq entry/exit

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Message-ID: <alpine.DEB.2.00.0903160934010.26431@gandalf.stny.rr.com>
Date:	Mon, 16 Mar 2009 09:34:57 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
cc:	Jason Baron <jbaron@...hat.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, acme@...stprotocols.net,
	fweisbec@...il.com, fche@...hat.com, peterz@...radead.org
Subject: Re: [Patch 2/2] tracepoints for softirq entry/exit - tracepoints


On Fri, 13 Mar 2009, Mathieu Desnoyers wrote:

> * Jason Baron (jbaron@...hat.com) wrote:
> > 
> > introduce softirq entry/exit tracepoints. These are useful for
> > augmenting existing tracers, and to figure out softirq frequencies and
> > timings.
> > 
> > Signed-off-by: Jason Baron <jbaron@...hat.com>
> > 
> > ---
> > 
> >  include/trace/irq_event_types.h |   12 ++++++++++++
> >  kernel/softirq.c                |    7 ++++++-
> >  2 files changed, 18 insertions(+), 1 deletions(-)
> > 
> > 
> > diff --git a/include/trace/irq_event_types.h b/include/trace/irq_event_types.h
> > index 214bb92..38b4bdd 100644
> > --- a/include/trace/irq_event_types.h
> > +++ b/include/trace/irq_event_types.h
> > @@ -40,4 +40,16 @@ TRACE_EVENT(irq_handler_exit,
> >  		  __entry->irq, __entry->ret ? "handled" : "unhandled")
> >  );
> >  
> > +TRACE_FORMAT(irq_softirq_entry,
> > +	TP_PROTO(struct softirq_action *h, struct softirq_action *vec),
> > +	TP_ARGS(h, vec),
> > +	TP_FMT("softirq=%d action=%s", h - vec, softirq_to_name[h-vec])
> > +	);
> > +
> > +TRACE_FORMAT(irq_softirq_exit,
> > +	TP_PROTO(struct softirq_action *h, struct softirq_action *vec),
> > +	TP_ARGS(h, vec),
> > +	TP_FMT("softirq=%d action=%s", h - vec, softirq_to_name[h-vec])
> 
> The softirq tracepoints are a good idea indeed (I have similar ones in
> the LTTng tree). My main concern is about the fact that you output the
> softirq name in plain text to the trace buffers. I would rather prefer
> to save only the softirq (h-vec) into the trace and dump the mapping
> (h-vec) to name only once, so we can save precious trace bytes.

The TP_FMT is only used by those tracers that want to use it. Any tracer 
can still hook directly to the trace point and do what every they want.

-- Steve
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