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

[James Clark <james.clark@linaro.org>]

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