linux-kernel - Re: [PATCH v4 3/3] tracing: add additional marks to signal very large delay

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Date:	Wed, 19 Nov 2014 13:35:15 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	byungchul.park@....com
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	seungho1.park@....com, jolsa@...hat.com
Subject: Re: [PATCH v4 3/3] tracing: add additional marks to signal very
 large delay

On Tue, 18 Nov 2014 14:57:26 +0900
byungchul.park@....com wrote:

> From: Byungchul Park <byungchul.park@....com>
> 
> Currently, some tracers tracing latency print "!" or "+" just after time
> to signal overhead, depending on the interval between events. Even it is
> usually enough to do that, we sometimes need to be signaled for bigger
> interval than 100 micro seconds.
> 
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> ---
>  Documentation/trace/ftrace.txt |    8 +++++---
>  kernel/trace/trace_output.c    |   23 ++++++++++++++++++-----
>  2 files changed, 23 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
> index f827e2f..64efb3e 100644
> --- a/Documentation/trace/ftrace.txt
> +++ b/Documentation/trace/ftrace.txt
> @@ -680,9 +680,11 @@ The above is mostly meaningful for kernel developers.
>  	 needs to be fixed to be only relative to the same CPU.
>  	 The marks are determined by the difference between this
>  	 current trace and the next trace.
> -	  '!' - greater than preempt_mark_thresh (default 100)
> -	  '+' - greater than 1 microsecond
> -	  ' ' - less than or equal to 1 microsecond.
> +	  '$' - greater than 1 second
> +	  '#' - greater than 1000 microsecond
> +	  '!' - greater than 100 microsecond
> +	  '+' - greater than 10 microsecond
> +	  ' ' - less than or equal to 10 microsecond.
>  
>    The rest is the same as the 'trace' file.
>  
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index c6977d5..3fd3017 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -124,7 +124,7 @@ ftrace_print_symbols_seq(struct trace_seq *p, unsigned long val,
>  
>  	if (ret == (const char *)(trace_seq_buffer_ptr(p)))
>  		trace_seq_printf(p, "0x%lx", val);
> -		
> +
>  	trace_seq_putc(p, 0);
>  
>  	return ret;
> @@ -471,7 +471,21 @@ lat_print_generic(struct trace_seq *s, struct trace_entry *entry, int cpu)
>  	return trace_print_lat_fmt(s, entry);
>  }
>  
> -static unsigned long preempt_mark_thresh_us = 100;
> +#undef MARK
> +#define MARK(v, s) {.val = v, .sym = s}
> +static const struct trace_mark mark[] = {
> +	MARK(1000000000ULL	, '$'), /* 1 sec */
> +	MARK(1000000ULL		, '#'), /* 1000 usecs */
> +	MARK(100000ULL		, '!'), /* 100 usecs */
> +	MARK(10000ULL		, '+'), /* 10 usecs */
> +	MARK(0ULL		, ' '), /* 0 usecs */
> +};
> +#undef MARK
> +
> +static inline char find_trace_mark(unsigned long long d)
> +{
> +	return trace_duration_mark(d, mark, ARRAY_SIZE(mark));
> +}

This is the exact same code as in function_graph tracer. Nuke the one
from function graph and make this one a non static function, and have
function graph tracer use it. trace_output.c is always compiled with
tracing.

In fact, remove all the code from trace.h, and move it here. Just
have this function be global and rename it to:

 trace_find_mark()

-- Steve


>  
>  static int
>  lat_print_timestamp(struct trace_iterator *iter, u64 next_ts)
> @@ -506,8 +520,7 @@ 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 ? '+' : ' ');
> +				find_trace_mark(rel_ts * NSEC_PER_USEC));
>  	} else { /* !verbose && !in_ns */
>  		return trace_seq_printf(s, " %4lld: ", abs_ts);
>  	}
> @@ -692,7 +705,7 @@ int register_ftrace_event(struct trace_event *event)
>  				goto out;
>  
>  		} else {
> -			
> +
>  			event->type = next_event_type++;
>  			list = &ftrace_event_list;
>  		}

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