linux-kernel - Re: [PATCH] perf ftrace: Make system wide the default target for latency subcommand

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Date:   Fri, 24 Mar 2023 18:39:25 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Yang Jihong <yangjihong1@...wei.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf ftrace: Make system wide the default target for
 latency subcommand

Hello,

On Thu, Mar 23, 2023 at 8:29 PM Yang Jihong <yangjihong1@...wei.com> wrote:
>
> If no target is specified for 'latency' subcommand, the execution fails
> because - 1 (invalid value) is written to set_ftrace_pid tracefs file.
> Make system wide the default target, which is the same as the default
> behavior of 'trace' subcommand.

I followed the convention to use -a for system-wide profiling.
Not sure if it's ok to make it default, but I don't object. :)

Thanks,
Namhyung

>
> Before the fix:
>
>   # perf ftrace latency -T schedule
>   failed to set ftrace pid
>
> After the fix:
>
>   # perf ftrace latency -T schedule
>   ^C#   DURATION     |      COUNT | GRAPH                                          |
>        0 - 1    us |          0 |                                                |
>        1 - 2    us |          0 |                                                |
>        2 - 4    us |          0 |                                                |
>        4 - 8    us |       2828 | ####                                           |
>        8 - 16   us |      23953 | ########################################       |
>       16 - 32   us |        408 |                                                |
>       32 - 64   us |        318 |                                                |
>       64 - 128  us |          4 |                                                |
>      128 - 256  us |          3 |                                                |
>      256 - 512  us |          0 |                                                |
>      512 - 1024 us |          1 |                                                |
>        1 - 2    ms |          4 |                                                |
>        2 - 4    ms |          0 |                                                |
>        4 - 8    ms |          0 |                                                |
>        8 - 16   ms |          0 |                                                |
>       16 - 32   ms |          0 |                                                |
>       32 - 64   ms |          0 |                                                |
>       64 - 128  ms |          0 |                                                |
>      128 - 256  ms |          4 |                                                |
>      256 - 512  ms |          2 |                                                |
>      512 - 1024 ms |          0 |                                                |
>        1 - ...   s |          0 |                                                |
>
> Fixes: 53be50282269 ("perf ftrace: Add 'latency' subcommand")
> Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
> ---
>  tools/perf/builtin-ftrace.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index d7fe00f66b83..fb1b66ef2e16 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -1228,10 +1228,12 @@ int cmd_ftrace(int argc, const char **argv)
>                 goto out_delete_filters;
>         }
>
> +       /* Make system wide (-a) the default target. */
> +       if (!argc && target__none(&ftrace.target))
> +               ftrace.target.system_wide = true;
> +
>         switch (subcmd) {
>         case PERF_FTRACE_TRACE:
> -               if (!argc && target__none(&ftrace.target))
> -                       ftrace.target.system_wide = true;
>                 cmd_func = __cmd_ftrace;
>                 break;
>         case PERF_FTRACE_LATENCY:
> --
> 2.30.GIT
>