Received-SPF: pass (google.com: domain of linux-kernel+bounces-180228-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: <20240510191423.2297538-1-yabinc@google.com> <20240510191423.2297538-4-yabinc@google.com>
 <CAM9d7chNz8-84m28q5qSLjUjZ=Ni1CA_JzbB_P+YJooLQd85YA@mail.gmail.com> <20240515085840.GD40213@noisy.programming.kicks-ass.net>
In-Reply-To: <20240515085840.GD40213@noisy.programming.kicks-ass.net>
From: Yabin Cui <yabinc@google.com>
Date: Wed, 15 May 2024 10:47:11 -0700
Message-ID: <CALJ9ZPOr7Jg8Vic9Ap5+jYqJVaLeV3DEJm3dAGBCLB9DL5EusQ@mail.gmail.com>
Subject: Re: [PATCH v4 3/3] perf/core: Check sample_type in perf_sample_save_brstack
To: Peter Zijlstra <peterz@infradead.org>
Cc: Namhyung Kim <namhyung@kernel.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@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Wed, May 15, 2024 at 1:58=E2=80=AFAM Peter Zijlstra <peterz@infradead.or=
g> wrote:
>
> On Fri, May 10, 2024 at 02:29:58PM -0700, Namhyung Kim wrote:
> > On Fri, May 10, 2024 at 12:14=E2=80=AFPM Yabin Cui <yabinc@google.com> =
wrote:
> > >
> > > Check sample_type in perf_sample_save_brstack() to prevent
> > > saving branch stack data when it isn't required.
> > >
> > > Suggested-by: Namhyung Kim <namhyung@kernel.org>
> > > Signed-off-by: Yabin Cui <yabinc@google.com>
> >
> > It seems powerpc has the similar bug, then you need this:
> >
> > Fixes: eb55b455ef9c ("perf/core: Add perf_sample_save_brstack() helper"=
)
>
> Is this really a bug? AFAICT it just does unneeded work, no?

It's not a bug. As I replied to Namhyuang, the powerpc code checks
sample_type before calling perf_sample_save_brstack().