linux-kernel - Re: [PATCH] tracing/ftrace: add an option to not print the context info for events

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Message-ID: <20090121090207.GA6374@nowhere>
Date:	Wed, 21 Jan 2009 10:02:08 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH] tracing/ftrace: add an option to not print the context
	info for events

On Tue, Jan 20, 2009 at 09:55:17PM -0500, Steven Rostedt wrote:
> 
> On Tue, 20 Jan 2009, Frederic Weisbecker wrote:
> 
> > Impact: make trace_event more convenient for tracers
> > 
> > All tracers (for the moment) that use the struct trace_event want to have
> > the context info printed before their own output: the pid/cmdline, cpu, and timestamp.
> > 
> > But some other tracers that want to implement their trace_event callbacks will
> > not necessary need these information.
> > 
> > This patch adds a new default-enabled trace option: TRACE_ITER_CONTEXT_INFO
> > When disabled through:
> > 
> > echo nocontext-info > /debugfs/tracing/trace_options
> 
> Thanks Frederic,
> 
> > 
> > The pid, cpu and timestamps headers will not be printed.
> > 
> > IE with the sched_switch tracer with context-info (default):
> > 
> >             bash-2935  [001]   100.356561:   2935:120:S ==> [001]     0:140:R <idle>
> >           <idle>-0     [000]   100.412804:      0:140:R   + [000]    11:115:S events/0
> >           <idle>-0     [000]   100.412816:      0:140:R ==> [000]    11:115:R events/0
> >         events/0-11    [000]   100.412829:     11:115:S ==> [000]     0:140:R <idle>
> > 
> > Without context-info:
> > 
> >   2935:120:S ==> [001]     0:140:R <idle>
> >      0:140:R   + [000]    11:115:S events/0
> >      0:140:R ==> [000]    11:115:R events/0
> >     11:115:S ==> [000]     0:140:R <idle>
> > 
> > A tracer can disable it at runtime by clearing the bit TRACE_ITER_CONTEXT_INFO in trace_flags.
> 
> How about adding another function method into the tracer, where it could 
> be what is printed at the start. The default being what is now printed. 
> This would be for trace and latency trace only.
> 



Good idea. So it would be something coupled with TRACE_TER_CONTEXT_INFO ?
I mean, without this option, the tracers would have to implement a dummy context_info
callback for these cases if they don't want any.


 
> > 
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > ---
> >  kernel/trace/trace.c |   61 ++++++++++++++++++++++++++++---------------------
> >  kernel/trace/trace.h |    3 +-
> >  2 files changed, 37 insertions(+), 27 deletions(-)
> > 
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index 220c264..a59ba48 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -227,7 +227,7 @@ static DECLARE_WAIT_QUEUE_HEAD(trace_wait);
> >  
> >  /* trace_flags holds trace_options default values */
> >  unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
> > -	TRACE_ITER_ANNOTATE;
> > +	TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO;
> >  
> >  /**
> >   * trace_wake_up - wake up tasks waiting for trace input
> > @@ -285,6 +285,7 @@ static const char *trace_options[] = {
> >  	"userstacktrace",
> >  	"sym-userobj",
> >  	"printk-msg-only",
> > +	"context-info",
> >  	NULL
> >  };
> >  
> > @@ -1487,21 +1488,23 @@ static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
> >  
> >  	test_cpu_buff_start(iter);
> >  
> > -	comm = trace_find_cmdline(iter->ent->pid);
> > -
> > -	t = ns2usecs(iter->ts);
> > -	usec_rem = do_div(t, 1000000ULL);
> > -	secs = (unsigned long)t;
> > -
> > -	ret = trace_seq_printf(s, "%16s-%-5d ", comm, entry->pid);
> > -	if (!ret)
> > -		return TRACE_TYPE_PARTIAL_LINE;
> > -	ret = trace_seq_printf(s, "[%03d] ", iter->cpu);
> > -	if (!ret)
> > -		return TRACE_TYPE_PARTIAL_LINE;
> > -	ret = trace_seq_printf(s, "%5lu.%06lu: ", secs, usec_rem);
> > -	if (!ret)
> > -		return TRACE_TYPE_PARTIAL_LINE;
> > +	if (trace_flags & TRACE_ITER_CONTEXT_INFO) {
> > +		comm = trace_find_cmdline(iter->ent->pid);
> > +
> > +		t = ns2usecs(iter->ts);
> > +		usec_rem = do_div(t, 1000000ULL);
> > +		secs = (unsigned long)t;
> > +
> > +		ret = trace_seq_printf(s, "%16s-%-5d ", comm, entry->pid);
> > +		if (!ret)
> > +			return TRACE_TYPE_PARTIAL_LINE;
> > +		ret = trace_seq_printf(s, "[%03d] ", iter->cpu);
> > +		if (!ret)
> > +			return TRACE_TYPE_PARTIAL_LINE;
> > +		ret = trace_seq_printf(s, "%5lu.%06lu: ", secs, usec_rem);
> > +		if (!ret)
> > +			return TRACE_TYPE_PARTIAL_LINE;
> > +	}
> 
> Or here we can do a:
> 
> 	if (iter->tr->context_info)
> 		ret = iter->tr->context_info(s, iter);
> 	else
> 		ret = default_context_info(s, iter);
> 
> This may give a tracer more control as to what to print for each entry.
> 
> -- Steve


Indeed, thanks!

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