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

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Message-ID: <b17b5edf-44bb-4734-c42a-8a498372ac8a@huawei.com>
Date:   Sat, 25 Mar 2023 11:29:02 +0800
From:   Yang Jihong <yangjihong1@...wei.com>
To:     Namhyung Kim <namhyung@...nel.org>
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 2023/3/25 9:39, Namhyung Kim wrote:
> 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 for the reply.

Yes, "perf ftrace latency" supports -a for system wide profiles.
Because "perf ftrace trace" defaults to system wide when no target is 
specified. Therefore, I sent the patch to check whether "latency" is 
consistent with the behavior of the "trace". :)

Thanks,
Yang.

> 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
>>
> .
>