perf ftrace: Select function/function_graph tracer automatically

The '-g/-G' options have already implied function_graph tracer should be
used instead of function tracer. So we don't need extra option
'--tracer' in this case.

This patch changes the behavior as below:

  - If '-g' or '-G' option is on, then function_graph tracer is used.
  - If '-T' or '-N' option is on, then function tracer is used.
  - The function_graph has priority over function tracer.
  - The option '--tracer' only take effect if neither -g/-G nor -T/-N
    is specified.

Here are some examples.

This will start tracing all functions using default 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

This will trace function vfs_read using function tracer:

  $ sudo perf ftrace -T vfs_read

Committer notes:

Using '-h -G' will tell what that option is about, so to further clarify
the above examples:

  # perf ftrace -h -G

    -G, --graph-funcs <func>	Set graph filter on given functions

  # perf ftrace -h -g

    -g, --nograph-funcs <func>	Set nograph filter on given functions

  # perf ftrace -h -T

    -T, --trace-funcs <func>	trace given functions only

  # perf ftrace -h -N

    -N, --notrace-funcs <func>	do not trace given functions

  #

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: http://lore.kernel.org/lkml/20200808023141.14227-2-changbin.du@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 23 insertions, 2 deletions

diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 2bfc1b0db536..048a11192b59 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -455,6 +455,23 @@ static void delete_filter_func(struct list_head *head)
 	}
 }
 
+static void select_tracer(struct perf_ftrace *ftrace)
+{
+	bool graph = !list_empty(&ftrace->graph_funcs) ||
+		     !list_empty(&ftrace->nograph_funcs);
+	bool func = !list_empty(&ftrace->filters) ||
+		    !list_empty(&ftrace->notrace);
+
+	/* The function_graph has priority over function tracer. */
+	if (graph)
+		ftrace->tracer = "function_graph";
+	else if (func)
+		ftrace->tracer = "function";
+	/* Otherwise, the default tracer is used. */
+
+	pr_debug("%s tracer is used\n", ftrace->tracer);
+}
+
 int cmd_ftrace(int argc, const char **argv)
 {
 	int ret;
@@ -479,11 +496,13 @@ 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 +524,8 @@ int cmd_ftrace(int argc, const char **argv)
 	if (!argc && target__none(&ftrace.target))
 		ftrace.target.system_wide = true;
 
+	select_tracer(&ftrace);
+
 	ret = target__validate(&ftrace.target);
 	if (ret) {
 		char errbuf[512];