linux-kernel - Re: [PATCH 1/3] tracing/stat: sort in ascending order

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Date:	Mon, 25 May 2009 17:42:32 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] tracing/stat: sort in ascending order

On Mon, May 25, 2009 at 04:46:09PM +0800, Li Zefan wrote:
> Currently the output of trace_stat/workqueues is totally reversed:
> 
>  # cat /debug/tracing/trace_stat/workqueues
>     ...
>     1       17       17      210       37   `-blk_unplug_work+0x0/0x57
>     1     3779     3779      181       11   |-cfq_kick_queue+0x0/0x2f
>     1     3796     3796                     kblockd/1:120
>     ...
> 
> The correct output should be:
> 
>     1     3796     3796                     kblockd/1:120
>     1     3779     3779      181       11   |-cfq_kick_queue+0x0/0x2f
>     1       17       17      210       37   `-blk_unplug_work+0x0/0x57
> 
> It's caused by "tracing/stat: replace linked list by an rbtree for sorting"
> (53059c9b67a62a3dc8c80204d3da42b9267ea5a0).
> 
> Though we can simply change dummy_cmp() to return -1 instead of 1, IMO
> it's better to always do ascending sorting in trace_stat.c, and leave each
> stat tracer to decide whether to sort in descending or ascending order.
> 
> [ Impact: fix the output of trace_stat/workqueue ]
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>


For now in stat tracing, the ascendent sorting is the most relevant.
Especially because we always want to see the highest problems first.

-1 (or < 0) usually means lower and 1 ( > 0) is higher.

I wonder what would most confuse the developers of stat tracers:

- to reverse these common sort values (-1 turn into "higher")
- keep the default ascendent sorting, which is not natural because the default
  is often descendent.

I don't know. 

Anyone else. Do you have a preference?

Thanks,

Frederic.


> ---
>  kernel/trace/ftrace.c       |   12 ++++++------
>  kernel/trace/trace_branch.c |    5 +++--
>  kernel/trace/trace_stat.c   |    6 +-----
>  3 files changed, 10 insertions(+), 13 deletions(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 140699a..3dd16bd 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -315,29 +315,29 @@ static void *function_stat_start(struct tracer_stat *trace)
>  }
>  
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> -/* function graph compares on total time */
> +/* function graph compares on total time in reverse order */
>  static int function_stat_cmp(void *p1, void *p2)
>  {
>  	struct ftrace_profile *a = p1;
>  	struct ftrace_profile *b = p2;
>  
> -	if (a->time < b->time)
> -		return -1;
>  	if (a->time > b->time)
> +		return -1;
> +	if (a->time < b->time)
>  		return 1;
>  	else
>  		return 0;
>  }
>  #else
> -/* not function graph compares against hits */
> +/* not function graph compares against hits in reverse order */
>  static int function_stat_cmp(void *p1, void *p2)
>  {
>  	struct ftrace_profile *a = p1;
>  	struct ftrace_profile *b = p2;
>  
> -	if (a->counter < b->counter)
> -		return -1;
>  	if (a->counter > b->counter)
> +		return -1;
> +	if (a->counter < b->counter)
>  		return 1;
>  	else
>  		return 0;
> diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> index 7a7a9fd..df58411 100644
> --- a/kernel/trace/trace_branch.c
> +++ b/kernel/trace/trace_branch.c
> @@ -301,9 +301,10 @@ static int annotated_branch_stat_cmp(void *p1, void *p2)
>  	percent_a = get_incorrect_percent(a);
>  	percent_b = get_incorrect_percent(b);
>  
> -	if (percent_a < percent_b)
> -		return -1;
> +	/* sort in descending order */
>  	if (percent_a > percent_b)
> +		return -1;
> +	if (percent_a < percent_b)
>  		return 1;
>  	else
>  		return 0;
> diff --git a/kernel/trace/trace_stat.c b/kernel/trace/trace_stat.c
> index 2e849b5..6efbcb4 100644
> --- a/kernel/trace/trace_stat.c
> +++ b/kernel/trace/trace_stat.c
> @@ -98,10 +98,6 @@ insert_stat(struct rb_root *root, struct stat_node *data, cmp_stat_t cmp)
>  {
>  	struct rb_node **new = &(root->rb_node), *parent = NULL;
>  
> -	/*
> -	 * Figure out where to put new node
> -	 * This is a descendent sorting
> -	 */
>  	while (*new) {
>  		struct stat_node *this;
>  		int result;
> @@ -110,7 +106,7 @@ insert_stat(struct rb_root *root, struct stat_node *data, cmp_stat_t cmp)
>  		result = cmp(data->stat, this->stat);
>  
>  		parent = *new;
> -		if (result >= 0)
> +		if (result < 0)
>  			new = &((*new)->rb_left);
>  		else
>  			new = &((*new)->rb_right);
> -- 
> 1.5.4.rc3
> 
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