Re: What do mean children of top ?

[taeung <treeze.taeung@gmail.com>]

On 03/04/2015 08:46 AM, Namhyung Kim wrote:
> Hi Arnaldo and Taewoong,
>
> On Tue, Mar 03, 2015 at 01:23:48PM -0300, Arnaldo Carvalho de Melo wrote:
>> Em Tue, Mar 03, 2015 at 02:04:47AM +0900, TaeWoong Song escreveu:
>>> Hi, perf users
>>>
>>> About
>>> The function perf_top_config() on builtin-top.c:
>>> It depend on whether top.children is ’true’ in perfconfig
>>> that whether ‘symbol_conf.cumulate_callchain’ is ’true’ or not.
>>> (when ‘top' only work with ‘—call-graph' )
>>>
>>> The output of ’top —call-graph fp’ is changed depending on  a boolean value of ‘symbol_conf.cumulate_callchain’.
>>>
>>> Do mean children of top relationship of calling functions which are parents or children ?
>>> Linked-ring of invoking functions ?
>>>
>>> I wanna exactly explain the effect of ‘top.children’ in perfconfig.
>>> Can anybody tell me the different between true and false on top.children ?
>>>
>>> If anybody a bit give hints me, I’ll appreciate it.
> The effect of top.children is same as report.children but just for perf top.
>
> The children here means that functions called from another function.
> Let me give you an example:
>
>    void foo(void) {
>      /* do something */
>    }
>
>    void bar(void) {
>      /* do something */
>      foo();
>    }
>
>    int main(void) {
>      bar()
>      return 0;
>    }
>
> In this case 'foo' is a child of 'bar', and 'bar' is an immediate
> child of 'main' so 'foo' also is a child of 'main'.  In other words,
> 'main' is a parent of 'foo' and 'bar'. and 'bar' is a parent of 'foo'.
> When you record with callchain you'll see something like this:
>
>   Overhead  Symbol
>   ........  .....................
>     60.00%  foo
>             |
>             --- foo
>                 bar
>                 main
>                 __libc_start_main
>
>     40.00%  bar
>             |
>             --- bar
>                 main
>                 __libc_start_main
>
> These percentage are 'self' overhead that came from the samples of the
> function themselves.  If you use --children, the overhead of children
> will be add to all of parents to calculate 'children' overhead.  In
> this case we'll see somethink like below:
>
>   Children      Self  Symbol
>   ........  ........  ....................
>    100.00%     0.00%  __libc_start_main
>             |
>             --- __libc_start_main
>
>    100.00%     0.00%  main
>             |
>             --- main
>                 __libc_start_main
>
>    100.00%    40.00%  bar
>             |
>             --- bar
>                 main
>                 __libc_start_main
>
>     60.00%    60.00%  foo
>             |
>             --- foo
>                 bar
>                 main
>                 __libc_start_main
>
> The first percentage is the children overhead and second is the self
> overhead.  As you can see, the children overhead is a sum of the self
> overhead and all (self) overhead of children.  It gives you an higher
> level view which function (including children) consumes cpu cycles (or
> other event) more.  And with '--call-graph caller', you'll see which
> children are called from this function.
>

Thank you very much.
I've clearly understanded about children in perf.

Thanks,
Taeung