Date: Thu, 4 Apr 2024 18:16:27 -0700
From: Ian Rogers <irogers@...gle.com>
To: "Liang, Kan" <kan.liang@...ux.intel.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 Thu, Apr 4, 2024 at 1:29 PM Liang, Kan <kan.liang@...ux.intel.com> wrote:
>
>
>
> 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.

Currently there is no concept of a metric group in the json except for
descriptions. Metrics and events share the same encoding, and the
deprecated flag belongs to the event.

> 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.

Why are you using No_group? I stand firm that it has no real use.

> 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.

What you are requesting here isn't something that is unreasonable, it
is just something unconnected with this change and requires a
reorganization of the json to facilitate. As such I consider it to be
something for follow up work.

I think if we're going to restructure metric groups it would be nice
to add a more tree-like structure which could be used to visualize
metrics better. For example here:
https://lore.kernel.org/lkml/20240314055919.1979781-11-irogers@google.com/
the metrics could be shown under a tree like:
ldst
 - ldst_total
   - ldst_total_loads
 - ldst_prcnt
   - ldst_prcnt_loads
   - ldst_prcnt_stores
 - ldst_ret_lds
   - ldst_ret_lds_1
   - ldst_ret_lds_2
   - ldst_ret_lds_3
 - ldst_ret_sts
   - ldst_ret_sts_1
   - ldst_ret_sts_2
   - ldst_ret_sts_3
 - ldst_ld_hit_swpf
 - ldst_atomic_lds

but again it is follow up work to do this. In this change I just
wanted a way to list all sensibly grouped metrics or metrics in a
group just on their own which doesn't require some kind of analysis of
metric groups. No_group has no use so let's just get rid of it.

Thanks,
Ian

> Thanks,
> Kan

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