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SubjectRe: [PATCH v2 2/4] perf ftrace: Add ftrace.tracer config option
Em Tue, Jan 31, 2017 at 08:38:29PM +0900, Taeung Song escreveu:
> Currently perf ftrace command will select 'function_graph' or 'function'.
> So add ftrace.tracer config option to select tracer

The above is confusing, I changed it to:

Currently 'perf ftrace' command allows selecting 'function_graph' or
'function', defaulting to 'function_graph'.

Add the ftrace.tracer config option to select the default tracer:

> # cat ~/.perfconfig
> [ftrace]
> tracer = function
>
> # perf ftrace usleep 123456 | head -10
> <...>-14450 [002] d... 10089.284231: finish_task_switch <-__schedule
> <...>-14450 [002] .... 10089.284232: finish_wait <-pipe_wait
> <...>-14450 [002] .... 10089.284232: mutex_lock <-pipe_wait
> <...>-14450 [002] .... 10089.284232: _cond_resched <-mutex_lock
>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
> ---
> tools/perf/builtin-ftrace.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index 414444d..00e228f 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -17,6 +17,7 @@
> #include "evlist.h"
> #include "target.h"
> #include "thread_map.h"
> +#include "util/config.h"
>
>
> #define DEFAULT_TRACER "function_graph"
> @@ -198,6 +199,26 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
> return done ? 0 : -1;
> }
>
> +static int perf_ftrace_config(const char *var, const char *value, void *cb)
> +{
> + struct perf_ftrace *ftrace = cb;
> +
> + if (!strcmp(var, "ftrace.tracer")) {
> + if (!strcmp(value, "function_graph"))
> + ftrace->tracer = DEFAULT_TRACER;
> + else if (!strcmp(value, "function"))
> + ftrace->tracer = "function";
> + else {
> + pr_err("Please select function_graph(default)"
> + "or function to use tracer.\n");
> + return -1;
> + }

If you use {} in the else case, use it in the other branch, also I
simplified it to be:

+ if (!strcmp(var, "ftrace.tracer")) {
+ if (!strcmp(value, "function_graph") ||
+ !strcmp(value, "function"))
+ ftrace->tracer = value;
+ else {
+ pr_err("Please select function_graph(default)"
+ "or function to use tracer.\n");
+ return -1;
+ }

As we know item->value will not go away (its a perf_config_item,
allocated and kept in that perf_config_set structure).

Also it doesn't make sense comparing against "function_graph" to set it
to DEFAULT_TRACER, as if we decide to change the DEFAULT_TRACER this
simply breaks.

Also you forgot to test by setting an invalid tracer, I did and noticed
that you forgot to add a space between "(default)" and "or ", please be
more careful with testing.

Also you are silently ignoring any unknown variable in this section, so
if someone has this:

cat ~/.perfconfig

[ftrace]

trace = function


I.e. forgets the 'r', it will keep using the current default,
"function_graph" till the user checks the config and adds that missing
'r'...

I haven't changed this because I think this is so common that we should
instead have a different error return for those config callbacks that
will tell perf_config() to say something like:

"unknown variable %s.%s\n", section_name, variable_name

- Arnaldo


> + return 0;
> + }
> +
> + return 0;
> +}
> +
> int cmd_ftrace(int argc, const char **argv, const char *prefix __maybe_unused)
> {
> int ret;
> @@ -218,6 +239,10 @@ int cmd_ftrace(int argc, const char **argv, const char *prefix __maybe_unused)
> OPT_END()
> };
>
> + ret = perf_config(perf_ftrace_config, &ftrace);
> + if (ret < 0)
> + return -1;
> +
> argc = parse_options(argc, argv, ftrace_options, ftrace_usage,
> PARSE_OPT_STOP_AT_NON_OPTION);
> if (!argc)
> --
> 2.7.4

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