linux-kernel - Re: [RFC][PATCH] tracing: Make branch trace display correct header

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Message-ID: <20090413164309.GJ5977@nowhere>
Date:	Mon, 13 Apr 2009 18:43:10 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Zhaolei <zhaolei@...fujitsu.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Tom Zanussi <tzanussi@...il.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] tracing: Make branch trace display correct header

On Mon, Apr 13, 2009 at 04:02:34PM +0800, Zhaolei wrote:
> Before patch:
>   # tracer: branch
>   #
>   #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
>   #              | |       |          |         |
>              <...>-2981  [000] 24008.872738: [  ok  ] trace_irq_handler_exit:irq_event_types.h:41
>              <...>-2981  [000] 24008.872742: [  ok  ] note_interrupt:spurious.c:229
>   ...
> 
> After patch:
> # tracer: branch
> #
> #           TASK-PID    CPU#    TIMESTAMP  CORRECT  FUNC:FILE:LINE
> #              | |       |          |         |       |
>            <...>-2985  [000] 26329.142970: [  ok  ] slab_free:slub.c:1776
>            <...>-2985  [000] 26329.142972: [  ok  ] trace_kmem_cache_free:kmem_event_types.h:191
>   ...
> 
> But it is not the best fix way.
> When format(length) of TASK-PID, CPU and TIMESTAMP chanegd in trace.c,
> other files who uses there fields need to changed for print right header line.
> 
> Maybe we can make a function to print header line of these 3 field:
> print_common_head()
> {
> 	seq_puts(s, "#           TASK-PID    CPU#    TIMESTAMP");
> }
> 
> and call this function in other files' print_header:
> static void branch_print_header(struct seq_file *s)
> {
> 	print_common_head();
> 	seq_puts(s, "  CORRECT  FUNC:FILE:LINE\n");
> }
> 
> But if header line is multi-line, this way can't work.
> 
> Another way is to export specific header-line content in other files:
> static void branch_print_header(char *buf, int len)
> {
> 	strcpy(buf, "  CORRECT  FUNC:FILE:LINE\n"
> 		    "     |            |\n"
> 		    );
> }
> And combile common-header and specific header in trace.c, then do seq_puts.
> But this seems too complex for tracing framework.
> 
> Similar problem exists in other tracers as sched_switch.


Indeed. I don't see any smart solution.
May be:

print_common_header_begin() // first line
print_common_header_end()   // second line with pipes

That's not pretty but at least it factorizes...

Hm?

Frederic.


 
> Signed-off-by: Zhao Lei <zhaolei@...fujitsu.com>
> ---
>  kernel/trace/trace_branch.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> index 8e64e60..7a7a9fd 100644
> --- a/kernel/trace/trace_branch.c
> +++ b/kernel/trace/trace_branch.c
> @@ -157,6 +157,13 @@ static enum print_line_t trace_branch_print(struct trace_iterator *iter,
>  	return TRACE_TYPE_HANDLED;
>  }
>  
> +static void branch_print_header(struct seq_file *s)
> +{
> +	seq_puts(s, "#           TASK-PID    CPU#    TIMESTAMP  CORRECT"
> +		"  FUNC:FILE:LINE\n");
> +	seq_puts(s, "#              | |       |          |         |   "
> +		"    |\n");
> +}
>  
>  static struct trace_event trace_branch_event = {
>  	.type		= TRACE_BRANCH,
> @@ -171,6 +178,7 @@ static struct tracer branch_trace __read_mostly =
>  #ifdef CONFIG_FTRACE_SELFTEST
>  	.selftest	= trace_selftest_startup_branch,
>  #endif /* CONFIG_FTRACE_SELFTEST */
> +	.print_header	= branch_print_header,
>  };
>  
>  __init static int init_branch_tracer(void)
> -- 1.5.5.3 
> 

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