linux-kernel - Re: [PATCH RFC/RFT] perf bpf skels: Stop using vmlinux.h generated from BTF, use subset of used structs + CO-RE. was Re: BPF skels in perf .Re: [GIT PULL] perf tools changes for v6.4

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Date:   Fri, 5 May 2023 17:49:35 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Jiri Olsa <olsajiri@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Namhyung Kim <namhyung@...nel.org>, Song Liu <song@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Clark Williams <williams@...hat.com>,
        Kate Carcia <kcarcia@...hat.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Adrian Hunter <adrian.hunter@...el.com>,
        Changbin Du <changbin.du@...wei.com>,
        Hao Luo <haoluo@...gle.com>, James Clark <james.clark@....com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Roman Lozko <lozko.roma@...il.com>,
        Stephane Eranian <eranian@...gle.com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Yang Jihong <yangjihong1@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        Paul Clarke <pc@...ibm.com>
Subject: Re: [PATCH RFC/RFT] perf bpf skels: Stop using vmlinux.h generated
 from BTF, use subset of used structs + CO-RE. was Re: BPF skels in perf .Re:
 [GIT PULL] perf tools changes for v6.4

Em Fri, May 05, 2023 at 01:46:30PM -0700, Ian Rogers escreveu:
> On Fri, May 5, 2023 at 1:43 PM Jiri Olsa <olsajiri@...il.com> wrote:
> >
> > On Fri, May 05, 2023 at 10:04:47AM -0700, Ian Rogers wrote:
> > > On Fri, May 5, 2023 at 9:56 AM Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> > > >
> > > > Em Fri, May 05, 2023 at 10:33:15AM -0300, Arnaldo Carvalho de Melo escreveu:
> > > > > Em Fri, May 05, 2023 at 01:03:14AM +0200, Jiri Olsa escreveu:
> > > > > That with the preserve_access_index isn't needed, we need just the
> > > > > fields that we access in the tools, right?
> > > >
> > > > I'm now doing build test this in many distro containers, without the two
> > > > reverts, i.e. BPF skels continue as opt-out as in my pull request, to
> > > > test build and also for the functionality tests on the tools using such
> > > > bpf skels, see below, no touching of vmlinux nor BTF data during the
> > > > build.
> > > >
> > > > - Arnaldo
> > > >
> > > > From 882adaee50bc27f85374aeb2fbaa5b76bef60d05 Mon Sep 17 00:00:00 2001
> > > > From: Arnaldo Carvalho de Melo <acme@...hat.com>
> > > > Date: Thu, 4 May 2023 19:03:51 -0300
> > > > Subject: [PATCH 1/1] perf bpf skels: Stop using vmlinux.h generated from BTF,
> > > >  use subset of used structs + CO-RE
> > > >
> > > > Linus reported a build break due to using a vmlinux without a BTF elf
> > > > section to generate the vmlinux.h header with bpftool for use in the BPF
> > > > tools in tools/perf/util/bpf_skel/*.bpf.c.
> > > >
> > > > Instead add a vmlinux.h file with the structs needed with the fields the
> > > > tools need, marking the structs with __attribute__((preserve_access_index)),
> > > > so that libbpf's CO-RE code can fixup the struct field offsets.
> > > >
> > > > In some cases the vmlinux.h file that was being generated by bpftool
> > > > from the kernel BTF information was not needed at all, just including
> > > > linux/bpf.h, sometimes linux/perf_event.h was enough as non-UAPI
> > > > types were not being used.
> > > >
> > > > To keep te patch small, include those UAPI headers from the trimmed down
> > > > vmlinux.h file, that then provides the tools with just the structs and
> > > > the subset of its fields needed for them.
> > > >
> > > > Testing it:
> > > >
> > > >   # perf lock contention -b find / > /dev/null
> >
> > I tested perf lock con -abv -L rcu_state sleep 1
> > and needed fix below
> >
> > jirka
> 
> I thought this was fixed by:
> https://lore.kernel.org/lkml/20230427234833.1576130-1-namhyung@kernel.org/
> but I think that is just in perf-tools-next.

Nope, we have it in perf-tools:

commit e53de7b65a3ca59af268c78df2d773f277f717fd
Author: Namhyung Kim <namhyung@...nel.org>
Date:   Thu Apr 27 16:48:32 2023 -0700

    perf lock contention: Fix struct rq lock access