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    SubjectRe: [RFC 00/13] kprobe/bpf: Add support to attach multiple kprobes
    On Tue,  4 Jan 2022 09:09:30 +0100
    Jiri Olsa <jolsa@redhat.com> wrote:

    > hi,
    > adding support to attach multiple kprobes within single syscall
    > and speed up attachment of many kprobes.
    >
    > The previous attempt [1] wasn't fast enough, so coming with new
    > approach that adds new kprobe interface.

    Yes, since register_kprobes() just registers multiple kprobes on
    array. This is designed for dozens of kprobes.

    > The attachment speed of of this approach (tested in bpftrace)
    > is now comparable to ftrace tracer attachment speed.. fast ;-)

    Yes, because that if ftrace, not kprobes.

    > The limit of this approach is forced by using ftrace as attach
    > layer, so it allows only kprobes on function's entry (plus
    > return probes).

    Note that you also need to multiply the number of instances.

    >
    > This patchset contains:
    > - kprobes support to register multiple kprobes with current
    > kprobe API (patches 1 - 8)
    > - bpf support ot create new kprobe link allowing to attach
    > multiple addresses (patches 9 - 14)
    >
    > We don't need to care about multiple probes on same functions
    > because it's taken care on the ftrace_ops layer.

    Hmm, I think there may be a time to split the "kprobe as an
    interface for the software breakpoint" and "kprobe as a wrapper
    interface for the callbacks of various instrumentations", like
    'raw_kprobe'(or kswbp) and 'kprobes'.
    And this may be called as 'fprobe' as ftrace_ops wrapper.
    (But if the bpf is enough flexible, this kind of intermediate layer
    may not be needed, it can use ftrace_ops directly, eventually)

    Jiri, have you already considered to use ftrace_ops from the
    bpf directly? Are there any issues?
    (bpf depends on 'kprobe' widely?)

    Thank you,

    --
    Masami Hiramatsu <mhiramat@kernel.org>

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