linux-kernel - Re: [RFC][PATCH 1/2] tracing: Add help of snapshot feature when snapshot is empty

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Date:	Thu, 07 Mar 2013 15:12:17 +0900
From:	Hiraku Toyooka <hiraku.toyooka.gu@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [RFC][PATCH 1/2] tracing: Add help of snapshot feature when snapshot
 is empty

(03/06/2013 10:49 PM), Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)"<srostedt@...hat.com>
> 
> When cat'ing the snapshot file, instead of showing an empty trace
> header like the trace file does, show how to use the snapshot
> feature.
> 
> Also, this is a good place to show if the snapshot has been allocated
> or not. Users may want to "pre allocate" the snapshot to have a fast
> "swap" of the current buffer. Otherwise, a swap would be slow and might
> fail as it would need to allocate the snapshot buffer, and that might
> fail under tight memory constraints.
> 
> Here's what it looked like before:
> 
>   # tracer: nop
>   #
>   # entries-in-buffer/entries-written: 0/0   #P:4
>   #
>   #                              _-----=> irqs-off
>   #                             / _----=> need-resched
>   #                            | / _---=> hardirq/softirq
>   #                            || / _--=> preempt-depth
>   #                            ||| /     delay
>   #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
>   #              | |       |   ||||       |         |
> 
> Here's what it looks like now:
> 
>   # tracer: nop
>   #
>   #
>   # * Snapshot is freed *
>   #
>   # Snapshot commands:
>   # echo 0 > snapshot : Clears and frees snapshot buffer
>   # echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.
>   #                      Takes a snapshot of the main buffer.
>   # echo 2 > snapshot : Clears snapshot buffer (but does not allocate)
>   #                      (Doesn't have to be '2' works with any number that
>   #                       is not a '0' or '1')
> 
> Cc: Hiraku Toyooka<hiraku.toyooka.gu@...achi.com>
> Signed-off-by: Steven Rostedt<rostedt@...dmis.org>
> ---

Acked-by: Hiraku Toyooka <hiraku.toyooka.gu@...achi.com>

>   kernel/trace/trace.c |   25 ++++++++++++++++++++++++-
>   1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index c2e2c23..9e3120b 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2400,6 +2400,27 @@ static void test_ftrace_alive(struct seq_file *m)
>   	seq_printf(m, "#          MAY BE MISSING FUNCTION EVENTS\n");
>   }
>   
> +#ifdef CONFIG_TRACER_MAX_TRACE
> +static void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter)
> +{
> +	if (iter->trace->allocated_snapshot)
> +		seq_printf(m, "#\n# * Snapshot is allocated *\n#\n");
> +	else
> +		seq_printf(m, "#\n# * Snapshot is freed *\n#\n");
> +
> +	seq_printf(m, "# Snapshot commands:\n");
> +	seq_printf(m, "# echo 0 > snapshot : Clears and frees snapshot buffer\n");
> +	seq_printf(m, "# echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.\n");
> +	seq_printf(m, "#                      Takes a snapshot of the main buffer.\n");
> +	seq_printf(m, "# echo 2 > snapshot : Clears snapshot buffer (but does not allocate)\n");
> +	seq_printf(m, "#                      (Doesn't have to be '2' works with any number that\n");
> +	seq_printf(m, "#                       is not a '0' or '1')\n");
> +}
> +#else
> +/* Should never be called */
> +static inline void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter) { }
> +#endif
> +
>   static int s_show(struct seq_file *m, void *v)
>   {
>   	struct trace_iterator *iter = v;
> @@ -2411,7 +2432,9 @@ static int s_show(struct seq_file *m, void *v)
>   			seq_puts(m, "#\n");
>   			test_ftrace_alive(m);
>   		}
> -		if (iter->trace && iter->trace->print_header)
> +		if (iter->snapshot && trace_empty(iter))
> +			print_snapshot_help(m, iter);
> +		else if (iter->trace && iter->trace->print_header)
>   			iter->trace->print_header(m);
>   		else
>   			trace_default_header(m);
> -- 1.7.10.4 .
> 

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