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Date: Wed, 06 Jan 2010 10:16:37 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Jiri Olsa <jolsa@...hat.com>
Cc: Lai Jiangshan <laijs@...fujitsu.com>,
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, 2010-01-06 at 14:08 +0100, Jiri Olsa wrote:
> 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()
?? And that is exactly what the above shows.
> >
> > 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.
Right.
Honestly, if you think about it, the "father_fun()" does call those
grandchild_fun() functions. Just indirectly. I don't find anything wrong
with this.
You get the same issue if gcc decides to inline a function, since those
inlined functions don't get traced either.
-- Steve
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