linux-kernel - Re: tracing: confusing output of function_graph when notrace function calls traceable function

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Message-ID: <20100106130806.GA7682@jolsa.lab.eng.brq.redhat.com>
Date:	Wed, 6 Jan 2010 14:08:06 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: tracing: confusing output of function_graph when notrace
 function calls traceable function

On Wed, Jan 06, 2010 at 06:44:02PM +0800, Lai Jiangshan wrote:
> cat <debugfs_dir>/tracing/trace
> you can get these at the end of the outputs:
> 
>  1)               |        nameidata_to_filp() {
>  1)               |          __dentry_open() {
>  1)               |            file_move() {
>  1)   0.834 us    |              _raw_spin_lock();
>  1)   0.926 us    |              _raw_spin_unlock();
>  1)   4.768 us    |            }
> 
> !!!! file_move() is really called by __dentry_open()
> 
>  1)               |            kmem_cache_alloc_notrace() {
>  1)   5.879 us    |              memset();
>  1) + 12.390 us   |            }
>  1)   1.025 us    |            mutex_lock();
>  1)               |            kmem_cache_alloc_notrace() {
>  1)   0.929 us    |              memset();
>  1)   3.329 us    |            }
>  1)   1.195 us    |            memcpy();
>  1)   1.026 us    |            __mutex_init();
> 
> !!!! the above are actually called by __tracing_open() which called by __dentry_open()
> (But at the first I was confused, I wondered why __dentry_open() calls them.)
> 
>  1)               |            kmem_cache_alloc_notrace() {
>  1)   0.978 us    |              memset();
>  1)   2.745 us    |            }
>  1)               |            __alloc_percpu() {
>  1)               |              pcpu_alloc() {
>  1)   1.053 us    |                mutex_lock();
>  1)   1.282 us    |                _raw_spin_lock_irqsave();
>  1)               |                pcpu_size_to_slot() {
>  1)   0.819 us    |                  __pcpu_size_to_slot();
>  1)   5.455 us    |                }
>  1)   1.135 us    |                pcpu_need_to_extend();
>  1)               |                pcpu_alloc_area() {
>  1)               |                  pcpu_chunk_slot() {
>  1)               |                    pcpu_size_to_slot() {
>  1)   0.813 us    |                      __pcpu_size_to_slot();
>  1)   2.535 us    |                    }
>  1)   8.349 us    |                  }
>  1)   1.160 us    |                  memmove();
>  1)               |                  pcpu_chunk_relocate() {
>  1)               |                    pcpu_chunk_slot() {
>  1)               |                      pcpu_size_to_slot() {
>  1)   0.803 us    |                        __pcpu_size_to_slot();
>  1)   2.478 us    |                      }
>  1)   4.129 us    |                    }
>  1)   8.583 us    |                  }
>  1) + 29.665 us   |                }
>  1)   1.038 us    |                _raw_spin_unlock_irqrestore();
>  1)   1.178 us    |                pcpu_next_pop();
>  1)   1.087 us    |                pcpu_chunk_addr();
>  1)   0.975 us    |                memset();
>  1)   0.821 us    |                pcpu_chunk_addr();
>  1)   0.943 us    |                memset();
>  1)   0.896 us    |                mutex_unlock();
>  1) + 75.625 us   |              }
>  1) + 77.453 us   |            }
> 
> !!!! the above are actually called by graph_trace_open() which called by __tracing_open()
> 
> == real graph ==:
> 
> father_fun()
>   child_fun()
>   notrace_child_fun()
>     grandchild_fun1()
>     grandchild_fun2()
> 
> ===function_graph shows===>
> 
> father_fun()
>   child_fun()
>   grandchild_fun1()
>   grandchild_fun2()
> 
> When the notrace function calls traceable function, function_graph will
> get wrong depth of functions, and show wrong graph.
> 
> Is there any method to fix it?
I dont think so..

AFAIK the depth computation is based on the traced functions, and there's
no other 'depth related' input apart from them.

jirka
> 
> Lai
> --
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