linux-kernel - Re: [PATCH] tracing: simplify print_graph

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Date:	Tue, 28 Jul 2009 17:53:24 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing: simplify print_graph_cpu()

On Tue, Jul 28, 2009 at 08:26:06PM +0800, Lai Jiangshan wrote:
> 
> print_graph_cpu() is little over-designed.
> 
> And "log10_all" may be wrong when there are holes in cpu_online_mask:
> the max online cpu id > cpumask_weight(cpu_online_mask)
>
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index abf7c4a..e30472d 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -183,43 +183,19 @@ static void graph_trace_reset(struct trace_array *tr)
>  	unregister_ftrace_graph();
>  }
>  
> -static inline int log10_cpu(int nb)
> -{
> -	if (nb / 100)
> -		return 3;
> -	if (nb / 10)
> -		return 2;
> -	return 1;
> -}
> +static int max_bytes_for_cpu;
>  
>  static enum print_line_t
>  print_graph_cpu(struct trace_seq *s, int cpu)
>  {
> -	int i;
>  	int ret;
> -	int log10_this = log10_cpu(cpu);
> -	int log10_all = log10_cpu(cpumask_weight(cpu_online_mask));
> -
>  
>  	/*
>  	 * Start with a space character - to make it stand out
>  	 * to the right a bit when trace output is pasted into
>  	 * email:
>  	 */
> -	ret = trace_seq_printf(s, " ");
> -
> -	/*
> -	 * Tricky - we space the CPU field according to the max
> -	 * number of online CPUs. On a 2-cpu system it would take
> -	 * a maximum of 1 digit - on a 128 cpu system it would
> -	 * take up to 3 digits:
> -	 */
> -	for (i = 0; i < log10_all - log10_this; i++) {
> -		ret = trace_seq_printf(s, " ");
> -		if (!ret)
> -			return TRACE_TYPE_PARTIAL_LINE;
> -	}
> -	ret = trace_seq_printf(s, "%d) ", cpu);
> +	ret = trace_seq_printf(s, " %*d) ", max_bytes_for_cpu, cpu);
>  	if (!ret)
>  		return TRACE_TYPE_PARTIAL_LINE;
>  
> @@ -919,6 +895,8 @@ static struct tracer graph_trace __read_mostly = {
>  
>  static __init int init_graph_trace(void)
>  {
> +	max_bytes_for_cpu = snprintf(NULL, 0, "%d", nr_cpu_ids - 1);


Nice trick :-)

Queued for .32, thanks!



> +
>  	return register_tracer(&graph_trace);
>  }
>  
> 
> 
> 
> 

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