On Wed, Jun 04, 2025 at 02:40:34PM -0700, Namhyung Kim wrote: > 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@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/. > 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. So, the comment in: tools/perf/util/bpf-event.c Is: * Synthesize PERF_RECORD_KSYMBOL and PERF_RECORD_BPF_EVENT for one bpf * program. One PERF_RECORD_BPF_EVENT is generated for the program. And * one PERF_RECORD_KSYMBOL is generated for each sub program. which is not so nicely worded tho :-\ "One KSYMBOL per program", followed by "one KSYMBOL per sub program". But that matches the referenced: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/events/core.c?h=v6.15#n9825 So, for these bpf_metadata_ variables, would that be strictly per program or would it be perf 'sub program'? Couldn't get an answer from looking at tools/bpf/bpftool/prog.c, but seems to be with progs, not subprogs, i.e. just the PERF_RECORD_KSYMBOL associated with progs (not subprogs) will have those variables. But then it seems those variables _are_ associated with at least one PERF_RECORD_KSYMBOL, right? - Arnaldo > 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.
