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Date:   Thu, 6 Aug 2020 08:14:48 +0800
From:   Changbin Du <changbin.du@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Changbin Du <changbin.du@...il.com>, Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 01/18] perf ftrace: select function/function_graph
 tracer automatically

On Tue, Aug 04, 2020 at 09:51:15AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Sat, Jul 18, 2020 at 02:48:09PM +0800, Changbin Du escreveu:
> > The '-g/-G' options have already implied function_graph tracer should be
> > used instead of function tracer. So the extra option '--tracer' can be
> > killed.
> > 
> > This patch changes the behavior as below:
> >   - By default, function tracer is used.
> >   - If '-g' or '-G' option is on, then function_graph tracer is used.
> >   - The perf configuration item 'ftrace.tracer' is marked as deprecated.
> >   - The option '--tracer' is marked as deprecated.
> 
> You should try to be more granular, for instance, I think the decision
> to change the default is questionable, but could be acceptable.
> 
> But why deprecate the perf configuration for the default tracer?
> 
> Say people who already use 'perf ftrace ls' go and use with this patch
> and see that it changed the default from the function_graph tracer to
> the function tracer and disagree with you, they want the default to be
> the function graph tracer, know that there is (or there was) a
> ftrace.tracer in ~/.prefconfig, and then try that, only to find out that
> it is not possible, frustrating :-\
> 
> So can we please remove this deprecation of ftrace.tracer so that people
> used to how it was can get that behaviour back?
> 
Agreed. If no -F or -G is given, we can use the ftrace.tracer as default tracer.
Let me update it. Thanks.

> I'll look at the other patches so as to provide comments on all of
> them and to speed things up I may end up removing this deprecation of
> ftrace.tracer and apply the rest, we can always revisit parts that I
> remove.
> 
> - Arnaldo
> 
> > Here are some examples.
> > 
> > This will start tracing all functions using function tracer:
> >   $ sudo perf ftrace
> > 
> > This will trace all functions using function graph tracer:
> >   $ sudo perf ftrace -G '*'
> > 
> > This will trace function vfs_read using function graph tracer:
> >   $ sudo perf ftrace -G vfs_read
> > 
> > Signed-off-by: Changbin Du <changbin.du@...il.com>
> > 
> > ---
> > v3: remove default '*' for -G/-T.
> > ---
> >  tools/perf/Documentation/perf-config.txt |  5 -----
> >  tools/perf/Documentation/perf-ftrace.txt |  2 +-
> >  tools/perf/builtin-ftrace.c              | 15 ++++++++++-----
> >  3 files changed, 11 insertions(+), 11 deletions(-)
> > 
> > diff --git a/tools/perf/Documentation/perf-config.txt b/tools/perf/Documentation/perf-config.txt
> > index c7d3df5798e2..a25fee7de3b2 100644
> > --- a/tools/perf/Documentation/perf-config.txt
> > +++ b/tools/perf/Documentation/perf-config.txt
> > @@ -612,11 +612,6 @@ trace.*::
> >  		"libbeauty", the default, to use the same argument beautifiers used in the
> >  		strace-like sys_enter+sys_exit lines.
> >  
> > -ftrace.*::
> > -	ftrace.tracer::
> > -		Can be used to select the default tracer. Possible values are
> > -		'function' and 'function_graph'.
> > -
> >  llvm.*::
> >  	llvm.clang-path::
> >  		Path to clang. If omit, search it from $PATH.
> > diff --git a/tools/perf/Documentation/perf-ftrace.txt b/tools/perf/Documentation/perf-ftrace.txt
> > index b80c84307dc9..952e46669168 100644
> > --- a/tools/perf/Documentation/perf-ftrace.txt
> > +++ b/tools/perf/Documentation/perf-ftrace.txt
> > @@ -24,7 +24,7 @@ OPTIONS
> >  
> >  -t::
> >  --tracer=::
> > -	Tracer to use: function_graph or function.
> > +	Tracer to use: function_graph or function. This option is deprecated.
> >  
> >  -v::
> >  --verbose=::
> > diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> > index 2bfc1b0db536..5f53da87040d 100644
> > --- a/tools/perf/builtin-ftrace.c
> > +++ b/tools/perf/builtin-ftrace.c
> > @@ -27,7 +27,6 @@
> >  #include "util/cap.h"
> >  #include "util/config.h"
> >  
> > -#define DEFAULT_TRACER  "function_graph"
> >  
> >  struct perf_ftrace {
> >  	struct evlist		*evlist;
> > @@ -419,6 +418,7 @@ static int perf_ftrace_config(const char *var, const char *value, void *cb)
> >  	if (strcmp(var, "ftrace.tracer"))
> >  		return -1;
> >  
> > +	pr_warning("Configuration ftrace.tracer is deprecated\n");
> >  	if (!strcmp(value, "function_graph") ||
> >  	    !strcmp(value, "function")) {
> >  		ftrace->tracer = value;
> > @@ -459,7 +459,7 @@ int cmd_ftrace(int argc, const char **argv)
> >  {
> >  	int ret;
> >  	struct perf_ftrace ftrace = {
> > -		.tracer = DEFAULT_TRACER,
> > +		.tracer = "function",
> >  		.target = { .uid = UINT_MAX, },
> >  	};
> >  	const char * const ftrace_usage[] = {
> > @@ -469,7 +469,7 @@ int cmd_ftrace(int argc, const char **argv)
> >  	};
> >  	const struct option ftrace_options[] = {
> >  	OPT_STRING('t', "tracer", &ftrace.tracer, "tracer",
> > -		   "tracer to use: function_graph(default) or function"),
> > +		   "tracer to use: function or function_graph (This option is deprecated)"),
> >  	OPT_STRING('p', "pid", &ftrace.target.pid, "pid",
> >  		   "trace on existing process id"),
> >  	OPT_INCR('v', "verbose", &verbose,
> > @@ -479,11 +479,13 @@ int cmd_ftrace(int argc, const char **argv)
> >  	OPT_STRING('C', "cpu", &ftrace.target.cpu_list, "cpu",
> >  		    "list of cpus to monitor"),
> >  	OPT_CALLBACK('T', "trace-funcs", &ftrace.filters, "func",
> > -		     "trace given functions only", parse_filter_func),
> > +		     "trace given functions using function tracer",
> > +		     parse_filter_func),
> >  	OPT_CALLBACK('N', "notrace-funcs", &ftrace.notrace, "func",
> >  		     "do not trace given functions", parse_filter_func),
> >  	OPT_CALLBACK('G', "graph-funcs", &ftrace.graph_funcs, "func",
> > -		     "Set graph filter on given functions", parse_filter_func),
> > +		     "trace given functions using function_graph tracer",
> > +		     parse_filter_func),
> >  	OPT_CALLBACK('g', "nograph-funcs", &ftrace.nograph_funcs, "func",
> >  		     "Set nograph filter on given functions", parse_filter_func),
> >  	OPT_INTEGER('D', "graph-depth", &ftrace.graph_depth,
> > @@ -505,6 +507,9 @@ int cmd_ftrace(int argc, const char **argv)
> >  	if (!argc && target__none(&ftrace.target))
> >  		ftrace.target.system_wide = true;
> >  
> > +	if (!list_empty(&ftrace.graph_funcs) || !list_empty(&ftrace.nograph_funcs))
> > +		ftrace.tracer = "function_graph";
> > +
> >  	ret = target__validate(&ftrace.target);
> >  	if (ret) {
> >  		char errbuf[512];
> > -- 
> > 2.25.1
> > 
> 
> -- 
> 
> - Arnaldo

-- 
Cheers,
Changbin Du

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