linux-kernel - Re: [PATCH v7 00/10] perf record --off-cpu: Dump off-cpu samples directly

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Message-ID: <CAH0uvojpYb17k6=PeJ6bz9cj2RSYyiDccgm1jnYRGmx4Hw4C=Q@mail.gmail.com>
Date: Tue, 12 Nov 2024 12:03:09 -0800
From: Howard Chu <howardchu95@...il.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: peterz@...radead.org, namhyung@...nel.org, irogers@...gle.com, 
	mingo@...hat.com, mark.rutland@....com, james.clark@...aro.org, 
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org, adrian.hunter@...el.com, 
	kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 00/10] perf record --off-cpu: Dump off-cpu samples directly

Hello,

On Tue, Nov 12, 2024 at 11:56 AM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> On Tue, Nov 12, 2024 at 04:17:19PM -0300, Arnaldo Carvalho de Melo wrote:
> > I squashed the patch below and I'm trying to apply the other patches to do some
> > minimal testing on the feature itself, but the organization of the
> > patches needs some work.
>
> > +++ b/tools/perf/util/bpf_off_cpu.c
> > @@ -61,6 +61,9 @@ static int off_cpu_config(struct evlist *evlist)
> >  static void off_cpu_start(void *arg)
> >  {
> >       struct evlist *evlist = arg;
> > +     struct evsel *evsel;
> > +     struct perf_cpu pcpu;
> > +     int i;
> >
> >       /* update task filter for the given workload */
> >       if (skel->rodata->has_task && skel->rodata->uses_tgid &&
> > @@ -82,6 +85,8 @@ static void off_cpu_start(void *arg)
> >       }
> >
> >       perf_cpu_map__for_each_cpu(pcpu, i, evsel->core.cpus) {
> > +             int err;
> > +
> >               err = bpf_map__update_elem(skel->maps.offcpu_output, &pcpu.cpu, sizeof(__u32),
> >                                          xyarray__entry(evsel->core.fd, i, 0),
> >                                          sizeof(__u32), BPF_ANY);
>
> This is not enough, as it in the end tries to use that
> skel->maps.offcpu_output that is only introduced at a later patch, it
> seems, not checked yet, but explains the error below:
>
>   LD      /tmp/build/perf-tools-next/perf-test-in.o
>   AR      /tmp/build/perf-tools-next/libperf-test.a
>   CC      /tmp/build/perf-tools-next/util/parse-events.o
> util/bpf_off_cpu.c: In function ‘off_cpu_start’:
> util/bpf_off_cpu.c:90:54: error: ‘struct <anonymous>’ has no member named ‘offcpu_output’
>    90 |                 err = bpf_map__update_elem(skel->maps.offcpu_output, &pcpu.cpu, sizeof(__u32),
>       |                                                      ^
> make[4]: *** [/home/acme/git/perf-tools-next/tools/build/Makefile.build:106: /tmp/build/perf-tools-next/util/bpf_off_cpu.o] Error 1
> make[4]: *** Waiting for unfinished jobs....
> make[3]: *** [/home/acme/git/perf-tools-next/tools/build/Makefile.build:158: util] Error 2
> make[2]: *** [Makefile.perf:789: /tmp/build/perf-tools-next/perf-util-in.o] Error 2
> make[2]: *** Waiting for unfinished jobs....
>   CC      /tmp/build/perf-tools-next/pmu-events/pmu-events.o
>   LD      /tmp/build/perf-tools-next/pmu-events/pmu-events-in.o
> make[1]: *** [Makefile.perf:292: sub-make] Error 2
> make: *** [Makefile:119: install-bin] Error 2
> make: Leaving directory '/home/acme/git/perf-tools-next/tools/perf'
> ⬢ [acme@...lbox perf-tools-next]$
>
>
> Ok, at the end of the series it builds, and the 'perf test' entry
> introduced in this series passes:
>
> root@x1:~# perf test off
> 121: perf record offcpu profiling tests                              : Ok
> root@x1:~# perf test -v off
> 121: perf record offcpu profiling tests                              : Ok
> root@x1:~# perf test -vv off
> 121: perf record offcpu profiling tests:
> --- start ---
> test child forked, pid 1303134
> Checking off-cpu privilege
> Basic off-cpu test
> Basic off-cpu test [Success]
> Child task off-cpu test
> Child task off-cpu test [Success]
> Direct off-cpu test
> Direct off-cpu test [Success]
> ---- end(0) ----
> 121: perf record offcpu profiling tests                              : Ok
> root@x1:~#
>
> But the only examples I could find so far for this feature were on the
> 'perf test' at the end of this series.
>
> I think we need to have some examples in the 'perf-record' man page
> showing how to use it, explaining the whole process, etc.
>
> I'll continue testing it and trying to move things around so that it
> gets bisectable and testable step by step, documenting the whole
> process as I go, probably tomorrow.
>
> The series with my fixes is at:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git perf-off-cpu77918
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/log/?h=perf-off-cpu

Thank you, I'll use that as the base of v8 :), adding Ian's suggestions.

>
>
> - Arnaldo

Thanks,
Howard