linux-kernel - Re: [PATCH] ftrace: Access ret_stack->subtime only in the function profiler

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Message-ID: <20160830013441.GA13062@sejong>
Date:   Tue, 30 Aug 2016 10:34:41 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH] ftrace: Access ret_stack->subtime only in the function
 profiler

Hi Steve,

On Mon, Aug 29, 2016 at 04:07:00PM -0400, Steven Rostedt wrote:
> On Mon, 29 Aug 2016 12:05:18 +0900
> Namhyung Kim <namhyung@...nel.org> wrote:
> 
> > The subtime is used only for function profiler with function graph
> > tracer enabled.  Move the definition of subtime under
> > CONFIG_FUNCTION_PROFILER to reduce the memory usage.  Also move the
> > initialization of subtime into the graph entry callback.
> 
> Hmm, I think documentation needs to be updated. Although it was never
> implemented, I believe I added the subtime to not only work with the
> profiler, but also with the normal tracing (to have the time of the
> internal functions subtracted from the upper level functions). But it
> appears that part was never implemented.
> 
> I'm fine with the patch, or actually implementing what graph-time
> states in Documentation/ftrace.txt. If we take this patch, that comment
> needs to be made to only mention the profiler (and the option should
> only be shown when the profiler is enabled).

Ah, missed the documentation part.  To implement it in the normal
tracing, I think we need to add 'subtime' field to struct
ftrace_graph_ret which will increase disk size.  Are you ok with this?

Thanks,
Namhyung


> 
> > 
> > Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > ---
> >  include/linux/ftrace.h               | 2 ++
> >  kernel/trace/ftrace.c                | 6 ++++++
> >  kernel/trace/trace_functions_graph.c | 1 -
> >  3 files changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> > index 6f93ac46e7f0..b3d34d3e0e7e 100644
> > --- a/include/linux/ftrace.h
> > +++ b/include/linux/ftrace.h
> > @@ -794,7 +794,9 @@ struct ftrace_ret_stack {
> >  	unsigned long ret;
> >  	unsigned long func;
> >  	unsigned long long calltime;
> > +#ifdef CONFIG_FUNCTION_PROFILER
> >  	unsigned long long subtime;
> > +#endif
> >  #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> >  	unsigned long fp;
> >  #endif
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 84752c8e28b5..2050a7652a86 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -872,7 +872,13 @@ function_profile_call(unsigned long ip, unsigned long parent_ip,
> >  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> >  static int profile_graph_entry(struct ftrace_graph_ent *trace)
> >  {
> > +	int index = trace->depth;
> > +
> >  	function_profile_call(trace->func, 0, NULL, NULL);
> > +
> > +	if (index >= 0 && index < FTRACE_RETFUNC_DEPTH)
> > +		current->ret_stack[index].subtime = 0;
> > +
> >  	return 1;
> >  }
> >  
> > diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> > index 0cbe38a844fa..9c7ffa4df5a8 100644
> > --- a/kernel/trace/trace_functions_graph.c
> > +++ b/kernel/trace/trace_functions_graph.c
> > @@ -170,7 +170,6 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth,
> >  	current->ret_stack[index].ret = ret;
> >  	current->ret_stack[index].func = func;
> >  	current->ret_stack[index].calltime = calltime;
> > -	current->ret_stack[index].subtime = 0;
> >  #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
> >  	current->ret_stack[index].fp = frame_pointer;
> >  #endif
>