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Date: Fri, 5 May 2023 18:33:26 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Ian Rogers <irogers@...gle.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 10:43:36PM +0200, Jiri Olsa escreveu:
> 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
patch not applying trying to do it manually.
- Arnaldo
>
> ---
> From b12aea55f1171dc09cde2957f9019c84bda7adbb Mon Sep 17 00:00:00 2001
> From: Jiri Olsa <jolsa@...nel.org>
> Date: Fri, 5 May 2023 13:28:46 +0200
> Subject: [PATCH] perf tools: Fix lock_contention bpf program
>
> We need to define empty 'struct rq' so the runqueues gets
> resolved properly:
>
> # ./perf lock con -b
> libbpf: extern (var ksym) 'runqueues': incompatible types, expected [99] fwd rq, but kernel has [19783] struct rq
> libbpf: failed to load object 'lock_contention_bpf'
> libbpf: failed to load BPF skeleton 'lock_contention_bpf': -22
> Failed to load lock-contention BPF skeleton
>
> Also rq__old/rq__new need additional '_' so the suffix is ignored
> properly.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
> tools/perf/util/bpf_skel/lock_contention.bpf.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> index 8911e2a077d8..c2bf24c68c14 100644
> --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> @@ -416,13 +416,15 @@ int contention_end(u64 *ctx)
> return 0;
> }
>
> +struct rq {};
> +
> extern struct rq runqueues __ksym;
>
> -struct rq__old {
> +struct rq___old {
> raw_spinlock_t lock;
> } __attribute__((preserve_access_index));
>
> -struct rq__new {
> +struct rq___new {
> raw_spinlock_t __lock;
> } __attribute__((preserve_access_index));
>
> @@ -434,8 +436,8 @@ int BPF_PROG(collect_lock_syms)
>
> for (int i = 0; i < MAX_CPUS; i++) {
> struct rq *rq = bpf_per_cpu_ptr(&runqueues, i);
> - struct rq__new *rq_new = (void *)rq;
> - struct rq__old *rq_old = (void *)rq;
> + struct rq___new *rq_new = (void *)rq;
> + struct rq___old *rq_old = (void *)rq;
>
> if (rq == NULL)
> break;
> --
> 2.40.1
>
--
- Arnaldo
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