linux-kernel - Re: [PATCH v5 2/2] tracing: add additional marks to signal very large time

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Message-ID: <20141120084617.4219e135@gandalf.local.home>
Date:	Thu, 20 Nov 2014 08:46:17 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	byungchul.park@....com, mingo@...hat.com,
	linux-kernel@...r.kernel.org, seungho1.park@....com,
	jolsa@...hat.com
Subject: Re: [PATCH v5 2/2] tracing: add additional marks to signal very
 large time

On Thu, 20 Nov 2014 15:05:43 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> Hi Steve and Byungchul,
> 
> On Wed, 19 Nov 2014 20:06:04 -0500, Steven Rostedt wrote:
> > On Thu, 20 Nov 2014 09:15:35 +0900
> > byungchul.park@....com wrote:
> >> -static unsigned long preempt_mark_thresh_us = 100;
> >> +#undef MARK
> >> +#define MARK(v, s) {.val = v, .sym = s}
> >> +/* trace overhead mark */
> >> +static const struct trace_mark {
> >> +	unsigned long long	val; /* unit: nsec */
> >> +	char			sym;
> >> +} mark[] = {
> >> +	MARK(1000000000ULL	, '$'), /* 1 sec */
> >> +	MARK(1000000ULL		, '#'), /* 1000 usecs */
> >> +	MARK(100000ULL		, '!'), /* 100 usecs */
> >> +	MARK(10000ULL		, '+'), /* 10 usecs */
> >> +	MARK(0ULL		, ' '), /* 0 usecs */
> >> +};
> >> +#undef MARK
> >> +
> >> +char trace_find_mark(unsigned long long d)
> >> +{
> >> +	int i;
> >> +	int size = ARRAY_SIZE(mark);
> >> +
> >> +	for (i = 0; i < size; i++) {
> >> +		if (d >= mark[i].val)
> >> +			break;
> >> +	}
> >> +
> >> +	return (i == size)? ' ' : mark[i].sym;
> >
> > Change this to:
> >
> > 	/* The break from loop must have been hit */
> > 	if (WARN_ON_ONCE(i == size))
> > 		return ' ';
> 
> I think it's impossible since it's always true that 'd >= 0'.
> 

It is impossible if this code never changes. But we all know that
wont be the case :-)

-- Steve
 
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