Date: Thu, 4 Apr 2024 16:29:34 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v1] perf metrics: Remove the "No_group" metric group



On 2024-04-03 4:26 p.m., Ian Rogers wrote:
> On Wed, Apr 3, 2024 at 11:57 AM Liang, Kan <kan.liang@...ux.intel.com> wrote:
>>
>>
>>
>> On 2024-04-03 2:31 p.m., Ian Rogers wrote:
>>> On Wed, Apr 3, 2024 at 10:59 AM Liang, Kan <kan.liang@...ux.intel.com> wrote:
>>>>
>>>>
>>>>
>>>> On 2024-04-03 12:46 p.m., Ian Rogers wrote:
>>>>> Rather than place metrics without a metric group in "No_group" place
>>>>> them in a a metric group that is their name. Still allow such metrics
>>>>> to be selected if "No_group" is passed, this change just impacts perf
>>>>> list.
>>>>
>>>> So it looks like the "No_group" is not completely removed.
>>>> They are just not seen in the perf list, but users can still use it via
>>>> perf stat -M No_group, right?
>>>>
>>>> If so, why we want to remove it from perf list? Where can the end user
>>>> know which metrics are included in the No_group?
>>>>
>>>> If the No_group is useless, why not completely remove it?
>>>
>>> Agreed. For command line argument deprecation we usually keep the
>>> option but hide it from help with PARSE_OPT_HIDDEN, so I was trying to
>>> follow that pattern albeit that a metric group isn't a command line
>>> option it's an option to an option.
>>>
>>
>> Perf list has a deprecated option to show the deprecated events.
>> The "No_group" should be a deprecated metrics group.
>>
>> If so, to follow the same pattern, I think perf list should still
>> display the "No_group" with the --deprecated option at least.
> 
> Such metrics would be shown twice, once under No_group and once under
> a metric group of their name.
You mean with the --deprecated option?
Yes, that's because the old/deprecated metrics group (No_group) is not
complete removed. So both the new name and old/deprecated name are shown
with the --deprecated option. The metrics which belong to both groups
will be shown twice.

Without the --deprecated option, only the new group and its members are
shown.

> With deprecated events this isn't the
> case, you can only see them with --deprecated. Given we can see the
> metric without the No_group grouping, what is being added by having a
> No_group grouping? It feels entirely redundant and something we don't
> need to advertise.

I just want to have a generic pattern for deprecating a metrics/metrics
group that everybody can follow.

I treat the "No_group" as a normal metrics group name. So this patch is
to introduce a new name, and hide the old name. Both new and old names
can still be used.

If it's for a deprecated event, the expectation is to only see the new
name by default, and see both new name and old name with the
--deprecated option.

Now, if it's a generic deprecated metrics group, what's the expected
behavior? I prefer to follow the same pattern as a deprecated event.
If we do so, yes, there will be some redundancy with the --deprecated
option, since some members may belong to both old and new groups.
But I don't think it's an issue. It's normal that metrics belong to
different groups.

Thanks,
Kan

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