linux-kernel - Re: [PATCH 12/20] perf tools: Add ->sort() member to struct sort

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Date:	Fri, 16 May 2014 15:40:52 +0900
From:	Namhyung Kim <namhyung@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Don Zickus <dzickus@...hat.com>
Subject: Re: [PATCH 12/20] perf tools: Add ->sort() member to struct sort_entry

On Thu, 15 May 2014 15:43:10 +0200, Jiri Olsa wrote:
> On Mon, May 12, 2014 at 03:28:45PM +0900, Namhyung Kim wrote:
>
> SNIP
>
>> +static int64_t
>> +sort__sym_sort(struct hist_entry *left, struct hist_entry *right)
>> +{
>> +	if (!left->ms.sym || !right->ms.sym)
>> +		return cmp_null(left->ms.sym, right->ms.sym);
>> +
>> +	return strcmp(right->ms.sym->name, left->ms.sym->name);
>> +}
>
> why do we need just string comparison for sort?

Because we want to sort them in alphabetical order.

>
>> +
>>  static int _hist_entry__sym_snprintf(struct map *map, struct symbol *sym,
>>  				     u64 ip, char level, char *bf, size_t size,
>>  				     unsigned int width)
>> @@ -255,6 +271,7 @@ static int hist_entry__sym_snprintf(struct hist_entry *he, char *bf,
>>  struct sort_entry sort_sym = {
>>  	.se_header	= "Symbol",
>>  	.se_cmp		= sort__sym_cmp,
>> +	.se_sort	= sort__sym_sort,
>>  	.se_snprintf	= hist_entry__sym_snprintf,
>>  	.se_width_idx	= HISTC_SYMBOL,
>
> so when we insert entries into hists we use se_cmp to group them
> via hist_entry__cmp
>
> the we sort this hists based on output and use se_sort to group
> them via __hists__insert_output_entry
>
> why can't we use just cmp?

As I said, the output should be sorted by symbol name.  IOW, in order to
group entries in input stage, putting them into a correct group is
important, but for output stage, the order is also important.

Thanks,
Namhyung
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