[PATCH RFC v1 2/3] perf: Add perf_event_attr::config3

[Arnaldo Carvalho de Melo]

On August 31, 2022 4:06:40 PM GMT-03:00, Rob Herring <robh at kernel.org> wrote:
>On Thu, Aug 25, 2022 at 1:08 PM Rob Herring <robh at kernel.org> wrote:
>>
>> Arm SPEv1.2 adds another 64-bits of event filtering control. As the
>> existing perf_event_attr::configN fields are all used up for SPE PMU, an
>> additional field is needed. Add a new 'config3' field.
>
>In testing this, just exposing 'config3' in the format attributes
>causes the SPE PMU to be disabled. So we can't add this without
>breaking existing perf. Shouldn't perf just skip any format fields it
>doesn't know about?

Something it doesn't know about, even more at the main perf_event_attr level, may preclude it to grok new records.

"May" is the key word, as perf_event_hdr has a size field, maybe sometimes it's possible to do as you say.

If you're interested propose patches to make perf ignore things when possible.

- Arnaldo