linux-kernel - Re: [PATCH] tracing/ftrace: add an option to not print the context info for events

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Date:	Tue, 20 Jan 2009 21:55:17 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH] tracing/ftrace: add an option to not print the context
 info for events


On Tue, 20 Jan 2009, Frederic Weisbecker wrote:

> Impact: make trace_event more convenient for tracers
> 
> All tracers (for the moment) that use the struct trace_event want to have
> the context info printed before their own output: the pid/cmdline, cpu, and timestamp.
> 
> But some other tracers that want to implement their trace_event callbacks will
> not necessary need these information.
> 
> This patch adds a new default-enabled trace option: TRACE_ITER_CONTEXT_INFO
> When disabled through:
> 
> echo nocontext-info > /debugfs/tracing/trace_options

Thanks Frederic,

> 
> The pid, cpu and timestamps headers will not be printed.
> 
> IE with the sched_switch tracer with context-info (default):
> 
>             bash-2935  [001]   100.356561:   2935:120:S ==> [001]     0:140:R <idle>
>           <idle>-0     [000]   100.412804:      0:140:R   + [000]    11:115:S events/0
>           <idle>-0     [000]   100.412816:      0:140:R ==> [000]    11:115:R events/0
>         events/0-11    [000]   100.412829:     11:115:S ==> [000]     0:140:R <idle>
> 
> Without context-info:
> 
>   2935:120:S ==> [001]     0:140:R <idle>
>      0:140:R   + [000]    11:115:S events/0
>      0:140:R ==> [000]    11:115:R events/0
>     11:115:S ==> [000]     0:140:R <idle>
> 
> A tracer can disable it at runtime by clearing the bit TRACE_ITER_CONTEXT_INFO in trace_flags.

How about adding another function method into the tracer, where it could 
be what is printed at the start. The default being what is now printed. 
This would be for trace and latency trace only.


> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
>  kernel/trace/trace.c |   61 ++++++++++++++++++++++++++++---------------------
>  kernel/trace/trace.h |    3 +-
>  2 files changed, 37 insertions(+), 27 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 220c264..a59ba48 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -227,7 +227,7 @@ static DECLARE_WAIT_QUEUE_HEAD(trace_wait);
>  
>  /* trace_flags holds trace_options default values */
>  unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
> -	TRACE_ITER_ANNOTATE;
> +	TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO;
>  
>  /**
>   * trace_wake_up - wake up tasks waiting for trace input
> @@ -285,6 +285,7 @@ static const char *trace_options[] = {
>  	"userstacktrace",
>  	"sym-userobj",
>  	"printk-msg-only",
> +	"context-info",
>  	NULL
>  };
>  
> @@ -1487,21 +1488,23 @@ static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
>  
>  	test_cpu_buff_start(iter);
>  
> -	comm = trace_find_cmdline(iter->ent->pid);
> -
> -	t = ns2usecs(iter->ts);
> -	usec_rem = do_div(t, 1000000ULL);
> -	secs = (unsigned long)t;
> -
> -	ret = trace_seq_printf(s, "%16s-%-5d ", comm, entry->pid);
> -	if (!ret)
> -		return TRACE_TYPE_PARTIAL_LINE;
> -	ret = trace_seq_printf(s, "[%03d] ", iter->cpu);
> -	if (!ret)
> -		return TRACE_TYPE_PARTIAL_LINE;
> -	ret = trace_seq_printf(s, "%5lu.%06lu: ", secs, usec_rem);
> -	if (!ret)
> -		return TRACE_TYPE_PARTIAL_LINE;
> +	if (trace_flags & TRACE_ITER_CONTEXT_INFO) {
> +		comm = trace_find_cmdline(iter->ent->pid);
> +
> +		t = ns2usecs(iter->ts);
> +		usec_rem = do_div(t, 1000000ULL);
> +		secs = (unsigned long)t;
> +
> +		ret = trace_seq_printf(s, "%16s-%-5d ", comm, entry->pid);
> +		if (!ret)
> +			return TRACE_TYPE_PARTIAL_LINE;
> +		ret = trace_seq_printf(s, "[%03d] ", iter->cpu);
> +		if (!ret)
> +			return TRACE_TYPE_PARTIAL_LINE;
> +		ret = trace_seq_printf(s, "%5lu.%06lu: ", secs, usec_rem);
> +		if (!ret)
> +			return TRACE_TYPE_PARTIAL_LINE;
> +	}

Or here we can do a:

	if (iter->tr->context_info)
		ret = iter->tr->context_info(s, iter);
	else
		ret = default_context_info(s, iter);

This may give a tracer more control as to what to print for each entry.

-- Steve

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