linux-kernel - Re: [PATCH 05/22] tools lib traceevent: Add hrtimer plugin

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Date:	Sat, 23 Nov 2013 03:59:23 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 05/22] tools lib traceevent: Add hrtimer plugin

On Fri, 22 Nov 2013 23:33:29 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> 2013-11-21 (목), 12:01 +0100, Jiri Olsa:
> > Backporting hrtimer plugin.
> > 
> > Backported from Steven Rostedt's trace-cmd repo (HEAD 0f2c2fb):
> > git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/trace-cmd.git
> > 
> > This plugin adds function field resolving for following
> > tracepoint events:
> >   timer:hrtimer_expire_entry
> >   timer:hrtimer_start
> > 
> > The diff of 'perf script' output generated by old and new code:
> > (data was generated by 'perf record -e 'timer:hrtimer*' -a')
> > 
> > --- script.hrtimer.old
> > +++ script.hrtimer.new
> > -         swapper     0 [000] 27405.519092: timer:hrtimer_start: [FAILED TO PARSE] hrtimer=0xffff88021e20e800 function=0xffffffff810c0e10 expires=27398383000000 softexpires=27398383000000
> > +         swapper     0 [000] 27405.519103: timer:hrtimer_start: hrtimer=0xffff88021e20e800 function=tick_sched_timer expires=27398383000000 softexpires=27398383000000
> > -         swapper     0 [001] 27405.519544: timer:hrtimer_expire_entry: [FAILED TO PARSE] hrtimer=0xffff880211334058 now=27398294182491 function=0xffffffff81086f20
> > +         swapper     0 [001] 27405.519544: timer:hrtimer_expire_entry: hrtimer=0xffff880211334058 now=27398294182491 function=posix_timer_fn/0x0
> > 
> > Check the 'function' field is translated into the function name.
> 
> [SNIP]
> > +	if (!fn) {
> > +		trace_seq_printf(s, " function=MISSING");
> > +	} else {
> > +		unsigned long long function;
> > +		const char *func;
> > +
> > +		if (pevent_read_number_field(fn, data, &function))
> > +			trace_seq_printf(s, " function=INVALID");
> > +
> > +		func = pevent_find_function(pevent, function);
> > +
> > +		trace_seq_printf(s, " function=%s", func);
> 
> Shouldn't it be like below?
> 
> 		if (pevent_read_number_field(fn, data, &function))
> 			trace_seq_printf(s, " function=INVALID");
> 		else {
> 			func = pevent_find_function(pevent, function);
> 			trace_seq_printf(s, " function=%s", func);
> 		}
> 
> Otherwise it'll print "function=XXX" twice if pevent_read_number_field()
> failed.
> 

Nice catch, but lets keep the backport and fixes separate.

Actually, this was one of the first plugins I wrote, and since then, I
added a function tat does this for you. The proper change is to rip
this out and use:

	pevent_print_func_field()

instead. That function does the checks properly.

-- Steve
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