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From:   Hao Luo <haoluo@google.com>
Date:   Thu, 3 Mar 2022 11:43:46 -0800
Message-ID: <CA+khW7gyOGgqJjyuSjJMJ8+iQmozZ6VhSJ7exZF0gGLOeS5gog@mail.gmail.com>
Subject: Re: [PATCH bpf-next v1 4/9] bpf: Introduce sleepable tracepoints
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Yonghong Song <yhs@fb.com>, Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>,
        KP Singh <kpsingh@kernel.org>,
        Shakeel Butt <shakeelb@google.com>,
        Joe Burton <jevburton.kernel@gmail.com>,
        Tejun Heo <tj@kernel.org>, Josh Don <joshdon@google.com>,
        Stanislav Fomichev <sdf@google.com>, bpf <bpf@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Mar 2, 2022 at 6:29 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Mar 2, 2022 at 5:09 PM Yonghong Song <yhs@fb.com> wrote:
> >
> >
> >
> > On 3/2/22 1:30 PM, Alexei Starovoitov wrote:
> > > On Wed, Mar 2, 2022 at 1:23 PM Yonghong Song <yhs@fb.com> wrote:
> > >>
> > >>
> > >>
> > >> On 2/25/22 3:43 PM, Hao Luo wrote:
> > >>> Add a new type of bpf tracepoints: sleepable tracepoints, which allows
> > >>> the handler to make calls that may sleep. With sleepable tracepoints, a
> > >>> set of syscall helpers (which may sleep) may also be called from
> > >>> sleepable tracepoints.
> > >>
> > >> There are some old discussions on sleepable tracepoints, maybe
> > >> worthwhile to take a look.
> > >>
> > >> https://lore.kernel.org/bpf/20210218222125.46565-5-mjeanson@efficios.com/T/
> > >
> > > Right. It's very much related, but obsolete too.
> > > We don't need any of that for sleeptable _raw_ tps.
> > > I prefer to stay with "sleepable" name as well to
> > > match the rest of the bpf sleepable code.
> > > In all cases it's faultable.
> >
> > sounds good to me. Agree that for the bpf user case, Hao's
> > implementation should be enough.
>
> Just remembered that we can also do trivial noinline __weak
> nop function and mark it sleepable on the verifier side.
> That's what we were planning to do to trace map update/delete ops
> in Joe Burton's series.
> Then we don't need to extend tp infra.
> I'm fine whichever way. I see pros and cons in both options.

Joe is also cc'ed in this patchset, I will sync up with him on the
status of trace map work.

Alexei, do we have potentially other variants of tp? We can make the
current u16 sleepable a flag, so we can reuse this flag later when we
have another type of tracepoints.