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

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Message-ID: <20090315053301.GC20949@elte.hu>
Date:	Sun, 15 Mar 2009 06:33:01 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Jason Baron <jbaron@...hat.com>, rostedt@...dmis.org,
	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


* Mathieu Desnoyers <compudj@...stal.dyndns.org> 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 right solution is to change this tracepoint to TRACE_EVENT() 
format. Jason, do you have time to do that?

	Ingo
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