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

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Message-ID: <CAP_z_Cg+mPpdzxg-d+VV5J9t7vTTNXQmKLdnfuNETm1H40OA+g@mail.gmail.com>
Date: Tue, 3 Jun 2025 14:54:50 -0700
From: Blake Jones <blakejones@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Ian Rogers <irogers@...gle.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	Chun-Tse Shao <ctshao@...gle.com>, Zhongqiu Han <quic_zhonhan@...cinc.com>, 
	James Clark <james.clark@...aro.org>, Charlie Jenkins <charlie@...osinc.com>, 
	Andi Kleen <ak@...ux.intel.com>, Dmitry Vyukov <dvyukov@...gle.com>, Leo Yan <leo.yan@....com>, 
	Yujie Liu <yujie.liu@...el.com>, Graham Woodward <graham.woodward@....com>, 
	Yicong Yang <yangyicong@...ilicon.com>, Ben Gainey <ben.gainey@....com>, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 2/3] perf: collect BPF metadata from existing BPF programs

Hi Namhyung,

On Tue, Jun 3, 2025 at 2:44 PM Namhyung Kim <namhyung@...nel.org> wrote:
> > > IIUC the metadata is collected for each BPF program which may have
> > > multiple subprograms.  Then this patch creates multiple PERF_RECORD_
> > > BPF_METADATA for each subprogram, right?
> > >
> > > Can it be shared using the BPF program ID?
> >
> > In theory, yes, it could be shared. But I want to be able to correlate them
> > with the corresponding PERF_RECORD_KSYMBOL events, and KSYMBOL events for
> > subprograms don't have the full-program ID, so I wouldn't be able to do that.
>
> It's unfortunate that KSYMBOL doesn't have the program ID, but IIRC the
> following BPF_EVENT should have it.  I think it's safe to think KSYMBOLs
> belong to the BPF_EVENT when they are from the same thread.

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.

Can you say more about why the duplicated records concern you?

Blake