Re: [PATCH bpf-next 00/13] bpf: Add tracing_multi link support for bpf progs

[Leon Hwang]

On 25/8/26 04:02, Andrii Nakryiko wrote:
> On Sun, Aug 23, 2026 at 10:00 PM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>>
>> On 22/8/26 01:46, Andrii Nakryiko wrote:
>>> On Sun, Aug 16, 2026 at 11:20 PM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>>>>
>>>> On 15/8/26 04:14, Andrii Nakryiko wrote:
>>>>> On Sun, Aug 9, 2026 at 8:01 AM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>>>>>>
>>>>>> Similar to the tracing_multi link support for kernel functions [1], add
>>>>>> support for bpf progs.
>>>>>>
>>>>>> When attaching to bpf progs, it must attaches to the target by text poke
>>>>>> way.
>>>>>>
>>>>>
>>>>> Please spend a bit more human effort on justification for the change
>>>>> and explaining your use case. In what case you'll be attaching to a
>>>>> large amount of BPF programs such that attachment speed-up (if there
>>>>> is any) matters.
>>>>
>>>> Will update the cover letter with justification and my use case.
>>>>
>>>> Here's my use case:
>>>>
>>>> I'm planning to enhance the function-graph feature of bpfsnoop [1]. It
>>>> will trace all bpf progs, including their subprogs, to draw a full
>>>> function call graph including bpf prog call sites.
>>>>
>>>
>>> fair enough, interesting use case, definitely outline that in the next
>>> revision (and provide before/after attach time as well for such use
>>> case, please)
>>>
>> Will include my use case.
>>
>> Implemented the attachment micro-benchmark. Here's the result on an
>> x86_64 16c16g VM:
>>
>> ./bench tracing-multi-attach-progs
>> Setting up benchmark 'tracing-multi-attach-progs'...
>> tracing-multi-attach-progs: prepared 1000 identical BPF program targets
>> tracing-multi-attach-progs: fentry created and attached 1000
>> programs/links in 679.324ms
>> tracing-multi-attach-progs: fentry.multi created one program and
>> attached one 1000-target link in 470.042ms
>> tracing-multi-attach-progs: fentry.multi creation/attachment speedup is
>> 1.45x
>>
>> The speedup 1.45x looks good. But attaching to 1000 progs via fentry
> 
> I'd say "meh". If 500ms is ok, 700ms is not that much more noticeable.
> 
Besides the attachment speedup, this series provides a way to attach to
multiple bpf progs via one link. The current revision reuses the
ftrace-based attachment, which relies on
CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS. In the next revision, it will get
rid of CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS with its own attachment
implementation. Hence, this series will be able to run on those arches
that have trampoline support.

Thanks,
Leon