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From: =?UTF-8?B?5qKm6b6Z6JGj?= <dongmenglong.8@bytedance.com>
Date: Wed, 21 Feb 2024 11:06:20 +0800
Message-ID: <CALz3k9jDsmNMrXdxdx152fgvBxDoY4Lj_xMf8z-pwPtpm75vXQ@mail.gmail.com>
Subject: Re: [External] Re: [PATCH bpf-next 0/5] bpf: make tracing program
 support multi-attach
To: Alexei Starovoitov <alexei.starovoitov@gmail.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, 
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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 <dong=
menglong.8@bytedance.com> wrote:
> >
> > On Wed, Feb 21, 2024 at 10:35=E2=80=AFAM =E6=A2=A6=E9=BE=99=E8=91=A3 <d=
ongmenglong.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 all=
owed to
> > > > > be attached to multiple hooks, and we have to create a BPF progra=
m for
> > > > > each kernel function, for which we want to trace, even through al=
l the
> > > > > program have the same (or similar) logic. This can consume extra =
memory,
> > > > > and make the program loading slow if we have plenty of kernel fun=
ction 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.

Both methods need to check the accessed args of the target.