linux-kernel - Re: [PATCH -tip RESEND 2/2] ftrace: Introduce nr_saved

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Message-ID: <878utez4a1.fsf@sejong.aot.lge.com>
Date:	Fri, 14 Feb 2014 13:50:30 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@...achi.com>
Cc:	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Ingo Molnar <mingo@...hat.com>, yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH -tip RESEND 2/2] ftrace: Introduce nr_saved_cmdlines I/F

Hi Yoshihiro,

On Thu, 13 Feb 2014 10:28:58 +0900, Yoshihiro YUNOMAE wrote:
> Introduce nr_saved_cmdlines I/F for changing the number of pid-comm list.
> saved_cmdlines can store 128 command names using SAVED_CMDLINES now, but
> 'no-existing processes' names are often lost in saved_cmdlines when we
> read trace data. So, by introducing nr_saved_cmdlines I/F, the rule storing
> 128 command names is changed to the command numbers defined users.
>
> When we write a value to nr_saved_cmdlines, the number of the value will
> be stored in pid-comm list:
>
> 	# echo 1024 > /sys/kernel/debug/tracing/nr_saved_cmdlines
>
> Here, 1024 command names are stored. The default number is 128 and the maximum
> number is PID_MAX_DEFAULT (=32768 if CONFIG_BASE_SMALL is not set). So, if we
> want to avoid to lose command names, we need to set 32768 to nr_saved_cmdlines.
>
> We can read the maximum number of the list:
>
> 	# cat /sys/kernel/debug/tracing/nr_saved_cmdlines
> 	128

[SNIP]
> @@ -3685,7 +3760,8 @@ static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
>  
>  	(*pos)++;
>  
> -	for (; ptr < &map_cmdline_to_pid[SAVED_CMDLINES]; ptr++) {
> +	for (; ptr < &savedcmd->map_cmdline_to_pid[savedcmd->cmdline_num];
> +	     ptr++) {
>  		if (*ptr == -1 || *ptr == NO_CMDLINE_MAP)
>  			continue;
>  
> @@ -3700,7 +3776,7 @@ static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
>  	void *v;
>  	loff_t l = 0;
>  
> -	v = &map_cmdline_to_pid[0];
> +	v = &savedcmd->map_cmdline_to_pid[0];
>  	while (l <= *pos) {
>  		v = saved_cmdlines_next(m, v, &l);
>  		if (!v)

Are you accessing the savecmd without trace_cmdline_lock?

Thanks,
Namhyung
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