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

[Namhyung Kim <namhyung@kernel.org>]

On Tue, Jun 03, 2025 at 03:29:35PM -0700, Blake Jones wrote:
> On Tue, Jun 3, 2025 at 3:10 PM Namhyung Kim <namhyung@kernel.org> 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/.

Thanks for sharing this.

I'm curious about the semantics of the KSYMBOL and BPF_EVENT.  And I
feel like there should be a connection between them.

Song and Jiri, what do you think?

Thanks,
Namhyung

> 
> > > 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