Re: [PATCH 2/3] perf: collect BPF metadata from existing BPF programs

[Blake Jones]

On Tue, Jun 3, 2025 at 3:10 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> > Hmmm. Is that documented and tested anywhere? Offhand it sounds like an
> > implementation detail that I wouldn't feel great about depending on -
> > certainly not without a strong guarantee that it wouldn't change.
>
> Good point.  Maybe BPF folks have some idea?
>
> Anyway the current code generates them together in a function.
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/events/core.c?h=v6.15#n9825

It certainly does, yeah. But I don't want to have that become another
instance of https://www.hyrumslaw.com/.

> > Can you say more about why the duplicated records concern you?
>
> More data means more chance to lost something.  I don't expect this is
> gonna be a practical concern but in general we should pursue less data.

That makes sense. In this case, it will only show up for BPF programs that
define "bpf_metadata_" variables (which is already an opt-in action), and
the number of variables a given program defines is likely to be quite small.
So I think the cost of the marginal increase in data generated is outweighed
by the usability and reliability benefits of being able to match these events
1:1 with the KSYMBOL events. If this proves to be a problem in practice,
it can be revisited.

Blake