From: Namhyung Kim <namhyung@kernel.org>
To: Ian Rogers <irogers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>,
Adrian Hunter <adrian.hunter@intel.com>,
Kan Liang <kan.liang@linux.intel.com>,
James Clark <james.clark@linaro.org>,
Zhongqiu Han <quic_zhonhan@quicinc.com>,
Yicong Yang <yangyicong@hisilicon.com>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
bpf@vger.kernel.org
Subject: Re: [PATCH v1 0/4] Pipe mode header dumping and minor space saving
Date: Wed, 25 Jun 2025 10:40:08 -0700 [thread overview]
Message-ID: <aFw0eBq2FBgy21IN@google.com> (raw)
In-Reply-To: <CAP-5=fUh5uJhbgdr0iYqB7DD=hZgdbAr+34yss=pCVwnWG08yQ@mail.gmail.com>
On Tue, Jun 24, 2025 at 01:15:13PM -0700, Ian Rogers wrote:
> On Tue, Jun 24, 2025 at 12:11 PM Namhyung Kim <namhyung@kernel.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@pipe [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@pipe [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 for the clarification, I was confused if it's fixing -I or -D. :)
Namhyung
next prev parent reply other threads:[~2025-06-25 17:40 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-07 6:12 [PATCH v1 0/4] Pipe mode header dumping and minor space saving Ian Rogers
2025-06-07 6:12 ` [PATCH v1 1/4] perf header: In pipe mode dump features without --header/-I Ian Rogers
2025-06-07 6:12 ` [PATCH v1 2/4] perf header: Allow tracing of attr events Ian Rogers
2025-06-07 6:12 ` [PATCH v1 3/4] perf header: Display message if BPF/BTF info is empty Ian Rogers
2025-06-07 6:12 ` [PATCH v1 4/4] perf header: Don't write empty BPF/BTF info Ian Rogers
2025-06-24 19:11 ` [PATCH v1 0/4] Pipe mode header dumping and minor space saving Namhyung Kim
2025-06-24 20:15 ` Ian Rogers
2025-06-25 17:40 ` Namhyung Kim [this message]
2025-06-26 17:41 ` Namhyung Kim
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