linux-kernel - Re: [PATCH v1] perf stat: Remove evlist__add_default

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Date: Tue, 9 Apr 2024 12:00:00 -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>,
 James Clark <james.clark@....com>, Yang Jihong <yangjihong1@...wei.com>,
 Kaige Ye <ye@...ge.org>, Yicong Yang <yangyicong@...ilicon.com>,
 K Prateek Nayak <kprateek.nayak@....com>, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf stat: Remove evlist__add_default_attrs use
 strings



On 2024-04-09 11:20 a.m., Ian Rogers wrote:
>>> +             ret = parse_events(evlist,
>>> +                             "context-switches,"
>>> +                             "cpu-migrations,"
>>> +                             "page-faults,"
>>> +                             "instructions,"
>>> +                             "cycles,"
>> "cycles",
>> "instructions",
>>
>> It's better to keep the original order.
> So the original order was:
> "cycles,"
> "stalled-cycles-frontend,"
> "stalled-cycles-backend,"
> "instructions"
>

Right. The stalled-* events are added between default_attrs0 and
default_attrs1.


> but many/most/all core PMUs don't provide the stalled-* events. At the
> programmer level instructions is the most fundamental thing, so having
> it last felt wrong hence moving it to be the first after the software
> events. My thought was, if we're going to reorder things then let's
> not do a half measure like:
> "cycles,"
> "instructions,"
> "stalled-cycles-frontend,"
> "stalled-cycles-backend"
> 
> let's just put things into their best order. It is obviously easy to
> change but having this way wasn't an accident. There's obviously
> subjectivity about whether cycles is more fundamental than
> instructions, my thought is that you get taught instructions first and
> that these take some number of cycles to execute, hence thinking
> instructions should have some priority in the output over cycles -
> some people may not even know what cycles means, it is hard enough
> when you do given the variety of different clocks 🙂
> 

My concern is that there may be someone who still relies on the std
output of perf stat default. So the output format/order matters for
them. Their scripts probably be broken if the order is changed.

Thanks,
Kan