linux-kernel - Re: [PATCH 1/7] perf stat: Initialize instead of overwriting clock event

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Message-ID: <CAP-5=fXYSLH9QcvdgV0D8Z-FoVxO25F_SN0BUdge4G_eCDDjZg@mail.gmail.com>
Date: Tue, 13 Aug 2024 07:43:25 -0700
From: Ian Rogers <irogers@...gle.com>
To: James Clark <james.clark@...aro.org>
Cc: linux-perf-users@...r.kernel.org, John Garry <john.g.garry@...cle.com>, 
	Will Deacon <will@...nel.org>, Mike Leach <mike.leach@...aro.org>, Leo Yan <leo.yan@...ux.dev>, 
	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>, "Liang, Kan" <kan.liang@...ux.intel.com>, 
	Yang Jihong <yangjihong1@...wei.com>, Ze Gao <zegao2021@...il.com>, 
	Dominique Martinet <asmadeus@...ewreck.org>, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/7] perf stat: Initialize instead of overwriting clock event

On Tue, Aug 13, 2024 at 7:38 AM James Clark <james.clark@...aro.org> wrote:
>
>
>
> On 13/08/2024 3:28 pm, Ian Rogers wrote:
> > On Tue, Aug 13, 2024 at 6:24 AM James Clark <james.clark@...aro.org> wrote:
> >>
> >> This overwrite relies on the clock event remaining at index 0 and is
> >> quite a way down from where the array is initialized, making it easy to
> >> miss. Just initialize it with the correct clock event to begin with.
> >>
> >> Signed-off-by: James Clark <james.clark@...aro.org>
> >> ---
> >>   tools/perf/builtin-stat.c | 7 +++----
> >>   1 file changed, 3 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> >> index 1f92445f7480..a65f58f8783f 100644
> >> --- a/tools/perf/builtin-stat.c
> >> +++ b/tools/perf/builtin-stat.c
> >> @@ -1817,7 +1817,9 @@ static int add_default_attributes(void)
> >>   {
> >>          struct perf_event_attr default_attrs0[] = {
> >>
> >> -  { .type = PERF_TYPE_SOFTWARE, .config = PERF_COUNT_SW_TASK_CLOCK             },
> >> +  { .type = PERF_TYPE_SOFTWARE, .config = target__has_cpu(&target) ?
> >> +                                               PERF_COUNT_SW_CPU_CLOCK :
> >> +                                               PERF_COUNT_SW_TASK_CLOCK        },
> >
> > Hand crafting perf_event_attr when we have an event name to
> > perf_event_atttr parser doesn't make sense. Doing things this way
> > means we need to duplicate logic between event parsing and these
> > default configurations. The default configurations are also using
> > legacy events which of course are broken on Apple ARM M? (albeit for
> > hardware events, here it is software). Event and metric parsing has to
> > worry about things like grouping topdown events. All-in-all let's have
> > one way to do things, event parsing, otherwise this code is going to
> > end up reinventing all the workarounds the event parsing has to have.
> > Lots of struct perf_event_attr also contribute to binary size.
> >
> > If you are worried about a cycles event being opened on arm_dsu PMUs,
> > there is this patch:
> > https://lore.kernel.org/lkml/20240525152927.665498-1-irogers@google.com/
> >
> > Thanks,
> > Ian
>
> Hi Ian,
>
> Is this comment related to this patch specifically or is it more of a
> general comment?
>
> This patch doesn't really make any actual changes other than move one
> line of code from one place to another.

James, this code is removed here:
https://lore.kernel.org/lkml/20240510053705.2462258-4-irogers@google.com/

Thanks,
Ian