linux-kernel - Re: [PATCH 2/3] perf ftrace: Add ftrace.tracer config option

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Date:   Fri, 27 Jan 2017 12:52:13 +0900
From:   Taeung Song <treeze.taeung@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Wang Nan <wangnan0@...wei.com>
Subject: Re: [PATCH 2/3] perf ftrace: Add ftrace.tracer config option



On 01/27/2017 03:58 AM, Arnaldo Carvalho de Melo wrote:
> Em Thu, Jan 26, 2017 at 06:35:38PM +0900, Taeung Song escreveu:
>> Currently perf ftrace command will select 'function_graph' or 'function'.
>> So add ftrace.tracer config option to select 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
>>       <...>-14450 [002] .... 10089.284233: generic_pipe_buf_confirm <-pipe_read
>>
>> Cc: Jiri Olsa <jolsa@...nel.org>
>> Cc: Namhyung Kim <namhyung@...nel.org>
>> Signed-off-by: Taeung Song <treeze.taeung@...il.com>
>> ---
>>  tools/perf/builtin-ftrace.c | 20 ++++++++++++++++++++
>>  1 file changed, 20 insertions(+)
>>
>> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
>> index 414444d..8df5416 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 +199,23 @@ 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
>> +			return -1;
>
> Please warn the user for invalid values and either just say that it is
> ignoring that setting or return -1 to make perf_config() return that,
> then make cmd_ftrace() check the return of perf_config() and bail out if
> you're not ignoring the config value.
>
> I think its better to do a: "pr_err()" in that "return -1" branch and
> make 'perf ftrace' fail, so that the user can fix its config before
> proceeding.
>


Arnaldo,

I modified this patch as below.

diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 8df5416..00e228f 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -208,8 +208,11 @@ static int perf_ftrace_config(const char *var, 
const char *value, void *cb)
                          ftrace->tracer = DEFAULT_TRACER;
                  else if (!strcmp(value, "function"))
                          ftrace->tracer = "function";
-                else
+                else {
+                        pr_err("Please select function_graph(default)"
+                               "or function to use tracer.\n");
                          return -1;
+                }
                  return 0;
          }

@@ -236,7 +239,9 @@ int cmd_ftrace(int argc, const char **argv, const 
char *prefix __maybe_unused)
          OPT_END()
          };

-        perf_config(perf_ftrace_config, &ftrace);
+        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);


But if setting wrong config value,
existing error message is printed in perf_config().

So output can be printed as follows

1) Two error messages

     # perf ftrace usleep 123456
     Please select function_graph(default)or function to use tracer.
     Error: wrong config key-value pair ftrace.tracer=functionds

2) Or only one error message in perf_config()
(if we don't "pr_err()" in that "return -1" branch)

     # perf ftrace usleep 123456
     Error: wrong config key-value pair ftrace.tracer=functionds


Which do you like better, 1) or 2) ?

Thanks,
Taeung