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

[Taeung Song]

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@jouet ~]# cat ~/.perfconfig
[ftrace]
        trace = function
[root@jouet ~]# perf ftrace usleep 1
Error: wrong config key-value pair ftrace.trace=function
[root@jouet ~]# cat ~/.perfconfig
[ftrace]
        tracer = functin
[root@jouet ~]# perf ftrace usleep 1
Please select "function_graph" (default) or "function"
Error: wrong config key-value pair ftrace.tracer=functin
[root@jouet ~]# cat ~/.perfconfig
[ftrace]
        tracer = function
[root@jouet ~]# 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@jouet ~]#

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