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

[James Clark]

On 13/08/2024 3:28 pm, Ian Rogers wrote:
> On Tue, Aug 13, 2024 at 6:24 AM James Clark <james.clark@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >   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@xxxxxxxxxx/
>
> 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