linux-kernel - Re: [PATCH v2 2/4] perf ftrace: Add ftrace.tracer config option

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Message-ID: <3a8d93cb-e988-cdf8-b5a7-eee48096202c@gmail.com>
Date:   Wed, 1 Feb 2017 16:27:02 +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 v2 2/4] perf ftrace: Add ftrace.tracer config option



On 01/31/2017 10:15 PM, Arnaldo Carvalho de Melo wrote:
> Em Tue, Jan 31, 2017 at 09:46:28AM -0300, Arnaldo Carvalho de Melo escreveu:
>> 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
>
> So I read a bit more the config code and ended up with this:
>
> static int perf_ftrace_config(const char *var, const char *value, void *cb)
> {
>         struct perf_ftrace *ftrace = cb;
>
>         if (prefixcmp(var, "ftrace."))
>                 return 0;
>
>         if (strcmp(var, "ftrace.tracer"))
>                 return -1;
>
>         if (!strcmp(value, "function_graph") ||
>             !strcmp(value, "function")) {
>                 ftrace->tracer = value;
>                 return 0;
>         }
>
> 	pr_err("Please select \"function_graph\" (default) or \"function\"\n");
>         return -1;
> }
>
> I.e. it will ignore variables for other sections and will stop at an unknown
> variable or value for ftrace.tracer:
>
> [root@...et ~]# cat ~/.perfconfig
> [ftrace]
> 	trace = function
> [root@...et ~]# perf ftrace usleep 1
> Error: wrong config key-value pair ftrace.trace=function
> [root@...et ~]# cat ~/.perfconfig
> [ftrace]
> 	tracer = functin
> [root@...et ~]# perf ftrace usleep 1
> Please select "function_graph" (default) or "function"
> Error: wrong config key-value pair ftrace.tracer=functin
> [root@...et ~]# cat ~/.perfconfig
> [ftrace]
> 	tracer = function
> [root@...et ~]# perf ftrace usleep 1 | head -5
>           <idle>-0     [000] d...  3855.820847: switch_mm_irqs_off <-__schedule
>            <...>-18550 [000] d...  3855.820849: finish_task_switch <-__schedule
>            <...>-18550 [000] d...  3855.820851: smp_irq_work_interrupt <-irq_work_interrupt
>            <...>-18550 [000] d...  3855.820851: irq_enter <-smp_irq_work_interrupt
>            <...>-18550 [000] d...  3855.820851: rcu_irq_enter <-irq_enter
> [root@...et ~]#
>

This is great!! I agonized about error message for
each other cases as above! But I think this is more precise than my patch!

Thanks,
Taeung