linux-kernel - Re: [PATCH] perf map: remove extra indirection from map_

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Date:   Fri, 23 Nov 2018 17:14:25 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Eric Saint-Etienne <eric.saint.etienne@...cle.com>
Cc:     Linux Kernel <linux-kernel@...r.kernel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Eric Saint-Etienne <eric.saintetienne@...il.com>
Subject: Re: [PATCH] perf map: remove extra indirection from map__find()

On Fri, Nov 23, 2018 at 02:42:39AM -0800, Eric Saint-Etienne wrote:
> A double pointer is used in map__find() where a single pointer is enough
> because the function doesn't affect the rbtree and the rbtree is locked.
> 
> Signed-off-by: Eric Saint-Etienne <eric.saint.etienne@...cle.com>

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka

> ---
>  tools/perf/util/map.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> index 354e545..3dac766 100644
> --- a/tools/perf/util/map.c
> +++ b/tools/perf/util/map.c
> @@ -846,19 +846,18 @@ void maps__remove(struct maps *maps, struct map *map)
>  
>  struct map *maps__find(struct maps *maps, u64 ip)
>  {
> -	struct rb_node **p, *parent = NULL;
> +	struct rb_node *p;
>  	struct map *m;
>  
>  	down_read(&maps->lock);
>  
> -	p = &maps->entries.rb_node;
> -	while (*p != NULL) {
> -		parent = *p;
> -		m = rb_entry(parent, struct map, rb_node);
> +	p = maps->entries.rb_node;
> +	while (p != NULL) {
> +		m = rb_entry(p, struct map, rb_node);
>  		if (ip < m->start)
> -			p = &(*p)->rb_left;
> +			p = p->rb_left;
>  		else if (ip >= m->end)
> -			p = &(*p)->rb_right;
> +			p = p->rb_right;
>  		else
>  			goto out;
>  	}
> -- 
> 1.8.3.1
>