Received-SPF: pass (google.com: domain of linux-kernel+bounces-73995-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Precedence: bulk
MIME-Version: 1.0
References: <20240220035105.34626-1-dongmenglong.8@bytedance.com>
 <CAADnVQ+E4ygZV6dcs8wj5FdFz9bfrQ=61235uiRoxe9RqQvR9Q@mail.gmail.com>
 <CALz3k9g__P+UdO2vLPrR5Y4sQonQJjOnGPNmhmxtRfhLKoV7Rg@mail.gmail.com>
 <CALz3k9h8CoAP8+ZmNvNGeXL9D_Q83Ovrubz9zHECr6C0TXuoVg@mail.gmail.com>
 <CAADnVQ+bOhh1R_eCoThyNg50dd4nA4-qhpXxOWheLeA_44npXg@mail.gmail.com> <CALz3k9jDsmNMrXdxdx152fgvBxDoY4Lj_xMf8z-pwPtpm75vXQ@mail.gmail.com>
In-Reply-To: <CALz3k9jDsmNMrXdxdx152fgvBxDoY4Lj_xMf8z-pwPtpm75vXQ@mail.gmail.com>
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Tue, 20 Feb 2024 19:18:25 -0800
Message-ID: <CAADnVQLtHQO9X7EBxe4x6YyAdQi33aqzTirTJff5epTcBatd3g@mail.gmail.com>
Subject: Re: [External] Re: [PATCH bpf-next 0/5] bpf: make tracing program
 support multi-attach
To: =?UTF-8?B?5qKm6b6Z6JGj?= <dongmenglong.8@bytedance.com>
Cc: Andrii Nakryiko <andrii@kernel.org>, Alexei Starovoitov <ast@kernel.org>, 
	Daniel Borkmann <daniel@iogearbox.net>, Martin KaFai Lau <martin.lau@linux.dev>, Eddy Z <eddyz87@gmail.com>, 
	Song Liu <song@kernel.org>, Yonghong Song <yonghong.song@linux.dev>, 
	John Fastabend <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>, 
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, 
	Mykola Lysenko <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>, mcoquelin.stm32@gmail.com, 
	alexandre.torgue@foss.st.com, Kui-Feng Lee <thinker.li@gmail.com>, 
	Feng Zhou <zhoufeng.zf@bytedance.com>, Dave Marchevsky <davemarchevsky@fb.com>, 
	Daniel Xu <dxu@dxuuu.xyz>, LKML <linux-kernel@vger.kernel.org>, bpf <bpf@vger.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@vger.kernel.org>, linux-stm32@st-md-mailman.stormreply.com, 
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Tue, Feb 20, 2024 at 7:06=E2=80=AFPM =E6=A2=A6=E9=BE=99=E8=91=A3 <dongme=
nglong.8@bytedance.com> wrote:
>
> On Wed, Feb 21, 2024 at 11:02=E2=80=AFAM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Tue, Feb 20, 2024 at 6:45=E2=80=AFPM =E6=A2=A6=E9=BE=99=E8=91=A3 <do=
ngmenglong.8@bytedance.com> wrote:
> > >
> > > On Wed, Feb 21, 2024 at 10:35=E2=80=AFAM =E6=A2=A6=E9=BE=99=E8=91=A3 =
<dongmenglong.8@bytedance.com> wrote:
> > > >
> > > > Hello,
> > > >
> > > > On Wed, Feb 21, 2024 at 9:24=E2=80=AFAM Alexei Starovoitov
> > > > <alexei.starovoitov@gmail.com> wrote:
> > > > >
> > > > > On Mon, Feb 19, 2024 at 7:51=E2=80=AFPM Menglong Dong
> > > > > <dongmenglong.8@bytedance.com> wrote:
> > > > > >
> > > > > > For now, the BPF program of type BPF_PROG_TYPE_TRACING is not a=
llowed to
> > > > > > be attached to multiple hooks, and we have to create a BPF prog=
ram for
> > > > > > each kernel function, for which we want to trace, even through =
all the
> > > > > > program have the same (or similar) logic. This can consume extr=
a memory,
> > > > > > and make the program loading slow if we have plenty of kernel f=
unction to
> > > > > > trace.
> > > > >
> > > > > Should this be combined with multi link ?
> > > > > (As was recently done for kprobe_multi and uprobe_multi).
> > > > > Loading fentry prog once and attaching it through many bpf_links
> > > > > to multiple places is a nice addition,
> > > > > but we should probably add a multi link right away too.
> > > >
> > > > I was planning to implement the multi link for tracing after this
> > > > series in another series. I can do it together with this series
> > > > if you prefer.
> > > >
> > >
> > > Should I introduce the multi link for tracing first, then this series=
?
> > > (Furthermore, this series seems not necessary.)
> >
> > What do you mean "not necessary" ?
> > Don't you want to still check that bpf prog access only N args
> > and BTF for these args matches across all attach points ?
>
> No, I means that if we should keep the
>
> "Loading fentry prog once and attaching it through many bpf_links to
> multiple places"
>
> and only keep the multi link.

I suspect supporting multi link only is better,
since the amount of kernel code to maintain will be less.