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

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

On 13/08/2024 3:43 pm, Ian Rogers wrote:
> On Tue, Aug 13, 2024 at 7:38 AM James Clark <james.clark@linaro.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@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, this code is removed here:
> https://lore.kernel.org/lkml/20240510053705.2462258-4-irogers@google.com/
> 
> Thanks,
> Ian

Oh I see yeah. We can still work on that change, merging this one 
doesn't necessarily have to block that one, it just makes this one a bit 
redundant when the other one gets done.

If I remember correctly in one of the last related discussions we 
thought that opening the cycles event as a sampling event should be a 
softer warning?

Actually it seems like the DSU cycles event is a non-issue specifically 
for perf stat because it will open successfully anyway? It was just in 
perf record where it was the issue?