Received-SPF: pass (google.com: domain of linux-kernel+bounces-165868-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Precedence: bulk
MIME-Version: 1.0
References: <20240425220509.1751260-1-yabinc@google.com> <CAM9d7cjQQ3AU7LFXYHEYukwSB9CvFQPtSzg3anfVg=maCP56AA@mail.gmail.com>
In-Reply-To: <CAM9d7cjQQ3AU7LFXYHEYukwSB9CvFQPtSzg3anfVg=maCP56AA@mail.gmail.com>
From: Yabin Cui <yabinc@google.com>
Date: Wed, 1 May 2024 17:10:23 -0700
Message-ID: <CALJ9ZPP-6bB4f4UP0Ydtsfty-PMRti_MqjZz5uazDXjuFtQsRQ@mail.gmail.com>
Subject: Re: [PATCH] perf/core: Trim dyn_size if raw data is absent
To: Namhyung Kim <namhyung@kernel.org>
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>, 
	Ian Rogers <irogers@google.com>, Adrian Hunter <adrian.hunter@intel.com>, 
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, 
	bpf <bpf@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi Namyung,

Thanks for reviewing the patch! Fixing the callsites is a better idea.
I have sent a v2 patch with name [PATCH v2] perf/core: Save raw sample
data conditionally based on sample type.
Rejecting tracepoint events without PERF_SAMPLE_RAW will break my use
case in Android. So I hope we don't do that.

Thanks,
Yabin


On Mon, Apr 29, 2024 at 2:59=E2=80=AFPM Namhyung Kim <namhyung@kernel.org> =
wrote:
>
> Hello Yabin,
>
> CC-ing the bpf list.
>
> On Thu, Apr 25, 2024 at 3:05=E2=80=AFPM Yabin Cui <yabinc@google.com> wro=
te:
> >
> > Currently, perf_tp_event() always allocates space for raw sample data,
> > even when the PERF_SAMPLE_RAW flag is not set. This leads to unused
> > spaces within generated sample records.
> >
> > This patch reduces dyn_size when PERF_SAMPLE_RAW is not present,
> > ensuring sample records use only the necessary amount of space.
>
> Right, it seems bpf-output and tracepoint events set the flags without
> checking PERF_SAMPLE_RAW.  Can you fix the callsites instead?
> Or we can add perf_event argument to perf_sample_save_raw_data()
> and check the flag inside.
>
> We might reject the output data when it's not opened with the flag.
> But I'm afraid it might break some existing BPF programs.
>
> Thanks,
> Namhyung
>
> >
> > Fixes: 0a9081cf0a11 ("perf/core: Add perf_sample_save_raw_data() helper=
")
> > Signed-off-by: Yabin Cui <yabinc@google.com>
> > ---
> >  kernel/events/core.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 724e6d7e128f..d68ecdc264d3 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -7688,6 +7688,10 @@ void perf_prepare_sample(struct perf_sample_data=
 *data,
> >                 data->raw =3D NULL;
> >                 data->dyn_size +=3D sizeof(u64);
> >                 data->sample_flags |=3D PERF_SAMPLE_RAW;
> > +       } else if ((data->sample_flags & ~sample_type) & PERF_SAMPLE_RA=
W) {
> > +               data->dyn_size -=3D data->raw->size + sizeof(u32);
> > +               data->raw =3D NULL;
> > +               data->sample_flags &=3D ~PERF_SAMPLE_RAW;
> >         }
> >
> >         if (filtered_sample_type & PERF_SAMPLE_BRANCH_STACK) {
> > --
> > 2.44.0.769.g3c40516874-goog
> >