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Message-ID: <CAP-5=fUh5uJhbgdr0iYqB7DD=hZgdbAr+34yss=pCVwnWG08yQ@mail.gmail.com>
Date: Tue, 24 Jun 2025 13:15:13 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: 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>, Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>,
James Clark <james.clark@...aro.org>, Zhongqiu Han <quic_zhonhan@...cinc.com>,
Yicong Yang <yangyicong@...ilicon.com>, linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v1 0/4] Pipe mode header dumping and minor space saving
On Tue, Jun 24, 2025 at 12:11 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Fri, Jun 06, 2025 at 11:12:34PM -0700, Ian Rogers wrote:
> > Pipe mode has no header and emits the data as if it were events. The
> > dumping of features was controlled by the --header/-I options which
> > makes little sense when they are events, normally traced when
> > dump_trace is true. Switch to making pipe feature events also be
> > traced with detail when other events are.
>
> I'm not sure I'm following. Are you saying the pipe mode doesn't
> support features with --header/-I option?
No, in pipe mode it currently shows just PERF_RECORD_FEATURE or
PERF_RECORD_ATTR for the details of the events containing these
things. The reason being that the dumping is controlled by separate
header flags (--header and -I). In patch 1 the commit message shows
the before:
```
$ perf record -o - -a sleep 1 | perf script -D -i -
...
0x2c8@...e [0x54]: event: 80
.
. ... raw event: size 84 bytes
. 0000: 50 00 00 00 00 00 54 00 05 00 00 00 00 00 00 00 P.....T.........
. 0010: 40 00 00 00 36 2e 31 35 2e 72 63 37 2e 67 61 64 @...6.15.rc7.gad
. 0020: 32 61 36 39 31 63 39 39 66 62 00 00 00 00 00 00 2a691c99fb......
. 0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
. 0040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
. 0050: 00 00 00 00 ....
0 0 0x2c8 [0x54]: PERF_RECORD_FEATURE
```
That is we have a feature "event" but there are no details there to
try to be able to understand the feature event. After the change this
becomes:
```
$ perf record -o - -a sleep 1 | perf script -D -i -
...
0x2c8@...e [0x54]: event: 80
.
. ... raw event: size 84 bytes
. 0000: 50 00 00 00 00 00 54 00 05 00 00 00 00 00 00 00 P.....T.........
. 0010: 40 00 00 00 36 2e 31 35 2e 72 63 37 2e 67 61 64 @...6.15.rc7.gad
. 0020: 32 61 36 39 31 63 39 39 66 62 00 00 00 00 00 00 2a691c99fb......
. 0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
. 0040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
. 0050: 00 00 00 00 ....
0 0 0x2c8 [0x54]: PERF_RECORD_FEATURE, # perf version : 6.15.rc7.gad2a691c99fb
```
So now in the dump trace output I can see this was a feature for perf
version and what that value is. There are often multiple
PERF_RECORD_FEATURE and PERF_RECORD_ATTR "events" and so the extra
trace output helps in being able to work out what's going on.
Thanks,
Ian
> It seems to work for me.
>
> $ git show
> commit be59dba332e1e8edd3e88d991ba0e4795ae2bcb2 (HEAD -> perf-testing)
> Author: Ian Rogers <irogers@...gle.com>
> Date: Tue Jun 17 15:33:56 2025 -0700
>
> libperf evsel: Add missed puts and asserts
>
> A missed evsel__close before evsel__delete was the source of leaking
> perf events due to a hybrid test. Add asserts in debug builds so that
> this shouldn't happen in the future. Add puts missing on the cpu map
> and thread maps.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> Link: https://lore.kernel.org/r/20250617223356.2752099-4-irogers@google.com
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>
> $ ./perf version
> perf version 6.16.rc3.gbe59dba332e1
>
> $ ./perf record -o- true | ./perf report -i- --header-only
> # ========
> # captured on : Tue Jun 24 12:06:38 2025
> # header version : 1
> # data offset : 0
> # data size : 0
> # feat offset : 0
> # ========
> #
> # hostname : bangji
> # os release : 6.12.20-1rodete1-amd64
> # perf version : 6.16.rc3.gbe59dba332e1
> # arch : x86_64
> # nrcpus online : 4
> # nrcpus avail : 8
> # cpudesc : 11th Gen Intel(R) Core(TM) i7-1185G7 @ 3.00GHz
> # cpuid : GenuineIntel,6,140,1
> # total memory : 32566540 kB
> # cmdline : /home/namhyung/project/linux/tools/perf/perf record -o- true
> # event : name = cycles:P, , id = { 369, 370, 371, 372 }, type = 0 (PERF_TYPE_HARDWARE), ...
> # CPU_TOPOLOGY info available, use -I to display
> # NUMA_TOPOLOGY info available, use -I to display
> # pmu mappings: cpu = 4, breakpoint = 5, cstate_core = 22, cstate_pkg = 23, hwmon_acpitz = 4294901760, ...
> # time of first sample : 0.000000
> # time of last sample : 0.000000
> # sample duration : 0.000 ms
> # MEM_TOPOLOGY info available, use -I to display
> # cpu pmu capabilities: branches=32, max_precise=3, pmu_name=icelake
> # intel_pt pmu capabilities: topa_multiple_entries=1, psb_cyc=1, single_range_output=1, ...
>
> >
> > The attr event in pipe mode had no dumping, wire this up and use the
> > existing perf_event_attr fprintf support.
> >
> > The header's bpf_prog_info or bpf_btf may be empty when written. If
> > they are empty just skip writing them to save space.
>
> These look good to me.
>
> Thanks,
> Namhyung
>
> >
> > Ian Rogers (4):
> > perf header: In pipe mode dump features without --header/-I
> > perf header: Allow tracing of attr events
> > perf header: Display message if BPF/BTF info is empty
> > perf header: Don't write empty BPF/BTF info
> >
> > tools/perf/util/header.c | 46 ++++++++++++++++++++++++++--------------
> > tools/perf/util/header.h | 1 +
> > 2 files changed, 31 insertions(+), 16 deletions(-)
> >
> > --
> > 2.50.0.rc0.604.gd4ff7b7c86-goog
> >
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