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

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Date:	Thu, 20 Nov 2014 15:05:43 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.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

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'.

Thanks,
Namhyung

>
> 	return mark[i].sym;
>
> -- Steve
>
>
>> +}
>>  
>>  static int
>>  lat_print_timestamp(struct trace_iterator *iter, u64 next_ts)
>> @@ -506,8 +532,7 @@ lat_print_timestamp(struct trace_iterator *iter, u64 next_ts)
>>  		return trace_seq_printf(
>>  				s, " %4lldus%c: ",
>>  				abs_ts,
>> -				rel_ts > preempt_mark_thresh_us ? '!' :
>> -				  rel_ts > 1 ? '+' : ' ');
>> +				trace_find_mark(rel_ts * NSEC_PER_USEC));
>>  	} else { /* !verbose && !in_ns */
>>  		return trace_seq_printf(s, " %4lld: ", abs_ts);
>>  	}
>> @@ -692,7 +717,7 @@ int register_ftrace_event(struct trace_event *event)
>>  				goto out;
>>  
>>  		} else {
>> -			
>> +
>>  			event->type = next_event_type++;
>>  			list = &ftrace_event_list;
>>  		}
--
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